Getting along with your boss can be great, especially if it can make the daily grind more enjoyable.

But at the end of the day, it's important to remember that your friend is still your superior, and there's a line you probably shouldn't cross. Honesty is the best policy in the workplace — but like any rule, this one has a few exceptions.

"It's important to be cautious with what you say to your boss, as even the slightest slip-up could make or break your career," said Ryan Kahn, founder of The Hired Group and author of "Hired! The Guide for the Recent Grad."

We talked to several workplace experts to gain their insight on phrases you shouldn't say to your boss, even if you're close. Responses ranged from simple questions such as "Can I be honest?" to how you ask for vacation days. Many of these aren't outright forbidden but should be carefully worded.

Aside from the obvious, like profanity and insults, here are some words and phrases you should never say to your boss, even if you're friends:

'That's impossible'

Your manager doesn't want to hear negativity or a lack of conviction. If you have concerns, state what they are and ask for input.

One of the best approaches in deciding whether to share your thoughts with your buddy boss or ask sensitive questions is to put yourself in their shoes, suggests Lynn Taylor, a workplace expert and the author of "Tame Your Terrible Office Tyrant: How to Manage Childish Boss Behavior and Thrive in Your Job."

"Do your comments and questions reflect a positive, can-do, and confident demeanor? Remember loose lips sink ships ­— so choose your words carefully when you feel challenged at work if you want to thrive in your career," she says.

'You're wrong'

Openly criticizing or pointing out your boss's mistake, even if they're a friend, is a punch to the ego, and it's a sure way to be excluded from future meetings or ignored the next time you raise your hand to speak, says Rosalinda Oropeza Randall, an etiquette and civility expert and author of "Don't Burp in the Boardroom."

If you feel your boss has made an error, there are better ways of addressing this, she explains.

You might say, "I may be misinformed on this one, but I was under the impression that ..." This prompts them to reconsider and correct the information if necessary without putting up their defenses. "Whatever phrase you use, say it with a helpful and cordial tone," Randall says.

'Can you ask so-and-so to do it?'

Relying on favoritism is not a good look. And anything that makes other people's jobs harder usually makes your boss's job harder, which they'll likely remember the next time promotions are discussed.

'I can't'

A can-do attitude is always a valued trait, and just because you're friends, it doesn't mean you'll get called on the next time an important project comes up.

'That's not part of my job'

No job description is ever set in stone. "As cross-functional teams remain the order of the day, you're expected to be flexible and make your boss's life easier," explains Taylor.

"As a side note, the more skill sets you accumulate, the more indispensable you are," she adds.

Saying that you're not willing to go beyond your role shows that you are also not willing to pitch in for the success of the company, says Kahn.

'No'

Your cooperation is expected, and so is a polite tone — even if you and your boss tend to joke around. "Telling your boss 'no' is a challenge — and is sometimes necessary — but it can be inappropriate if you don't phrase it well with an explanation," Taylor says.

"For example, if your boss says, 'Do you have time to work on the Smith project today?' you shouldn't just say, 'No.' Instead, try something like, 'Today will be a challenge if you still want me to focus on that company presentation. Would you prefer I work on this today instead?'"

'I don't know'

You may not have the answer to every question, but your best guess and a promise to find out is much better than a shrug of the shoulders, Taylor says. While friends have each others' backs, "anytime your boss would need to do the work for you, assume that's not a path you should take."

'I'll try'

Some people think that this is an acceptable response, as we all "try" to get things done to our best ability. But it leaves a manager feeling unsure, and when assignments are given, your boss is counting on you, usually with specific deadlines, says Taylor.

'I'm just gonna grab a couple coffee packets from the kitchen'

Believe it or not, pilfering office supplies can be a fireable offense, so admitting this to your buddy boss is a terrible idea.

You'd better believe that when push comes to shove, they're not going to put their own job on the line to protect yours.

'I'm not paid enough to do that'

This one is similar to "that's not part of my job."

Maybe you're just trying to be funny — or hint that you deserve a raise — but this phrase can come across as highly inappropriate and unprofessional, and it tells your boss that you're not willing to go above and beyond. 

'My breakup has got me all messed up. My heart's just not in it today.' 

Everyone has personal problems every now and then, and turning to friends for emotional support can help — but this should never come at the expense of your professionalism.

"This is when you might consider taking a 'sick day' or calling your mom for some love and tenderness," Randall says.

'How do I benefit from this?'

Sometimes your work involves helping others and other departments. Bosses have little tolerance for those who aren't team players, Taylor says.

'That's not what I heard'

Avoiding gossip and conjecture is a good idea, as it can backfire. If you're not sure about something, wait, or you risk appearing unprofessional.

'So, what should we do this weekend?'

Making plans with your boss outside of work is fine, but you should be discreet about it. Talking about your plans together in front of the entire office could make your coworkers jealous and lead to accusations of preferential treatment.

'I'm sorry, but...'

"The caveat essentially cancels any genuine apologetic sentiment," Taylor says. "A straight, 'I'm sorry. I'll be much more aware of this next time' is the expected response when you mess up."

'Well, I did my best'

If you made a mistake and that was your best, that doesn't speak highly of your abilities. The better response is that you'll get it right next time.

'I've tried that before'

Bosses have little tolerance for laziness. "Examine whether you really gave the option a shot before you shoot it down," Taylor suggests. "Your boss may have something else in mind."

Alternatively, explain that you appreciate the suggestion and tried XYZ with such-and-such as a result, but you would be glad to try something more effective.

'I just assumed that...'

That phrase causes frustration for many bosses, as they'd rather hear that you made an error in judgment and learned from it instead of excuses. "To err is human, but to defer blame is a career killer," Taylor says.

'It's really not my fault; it's so-and-so's fault'

The blame game is a treacherous path. If you're innocent, then explain why. Don't implicate others if you bear the primary responsibility, Taylor says.

"Taking responsibility is key," adds Kahn. "If you're always seen as someone pointing the finger, eventually your boss is going to question who is really to blame."

'If I don't hear from you, I'll just do...'

This has a threatening tone, and it certainly crosses the line into unprofessionalism. It's better to wait than be admonished later.

'I can't work with that person'

Not playing well with others isn't good in elementary school, nor is it acceptable in the workplace. It's assumed that you are capable of getting beyond personality conflicts in the interest of delivering excellent results, no preferential treatment required.

'He's a jerk'

You may be this candid with your friends at home, but you shouldn't be with your boss.

"The golden rule is something your boss expects you to observe, and casting aspersions on others has no redeeming value. It just reflects badly on you," Taylor says.

'Why does so-and-so always...?'

Whining is annoying, to friends and bosses alike. "If you have a gripe, better to ask how you can attain a certain privilege and leave others out of the discussion," Taylor suggests.

'I don't have a solution'

Don't tell the boss about problems without presenting potential solutions, says Kahn. "Leaders talk about solutions; followers talk about the problems."

'I'm bored'

"You may have a weak moment and share your boredom with the wrong person: your boss," says Taylor. "You're being paid to be productive and remain enthusiastic. It's your responsibility to find ways to make your job interesting."

'I've gotta tell you about last night's hookup!'

Sharing intimate stories at work may not be a wise move, Randall says.

"What if a coworker overhears the sizzling conversation? That may open you or your boss up to a sexual harassment or inappropriate conversation write-up," she explains.

'I'm pretty busy. Can it wait?'

It's your responsibility to ask your boss if priorities have changed, as your objectives must stay aligned with your manager's. "Priorities are rarely stagnant, so as in most cases, your better option is to ask if you should reshuffle them," Randall recommends.

'Can I leave early today since things are slow?'

It's fine if you have to leave early, but don't say it's because "things are slow" or you have "nothing to do."

"There are always more projects in the pipeline. Bosses want you to show initiative," Taylor says.

'I'm going to be out these days,' or 'I'm leaving early tomorrow'

Just because you're friends, it doesn't mean you should tell your boss you're going on vacation or leaving the office early. It's always best to ask politely.

Of course, you're not a child, so you don't have to phrase it as: "May I please take Monday, Tuesday, and Wednesday off?" Instead, try: "I was planning to take off Monday through Wednesday, and wanted to make sure that was okay with you."

'Can I be honest?'

"Your boss hopes you're honest 100% of the time, and what you're about to say is not an aberration," said Taylor.

'I heard John just got a raise/promotion.'

"If you're trying to get a raise or promotion, don't compare yourself to others," said Taylor. She added that while office gossip does exist, discussing others' promotions will "likely backfire," and it's better to approach your career goals "from a factual standpoint about yourself only."

'Maybe it's a generational thing.'

"Regardless of what generational category you fall into — Gen X, Y, Z or baby boomer — this phrase is just disparaging. Better to avoid any armchair analysis," said Taylor.

'I have confidence that you can do this.'

"While it's okay to compliment your boss occasionally, avoid offering patronizing props," said Taylor, "Especially if your strategy is to pass off work to them!"