"That's not my job." You know what? A lot of bosses are simple souls who think your job is to do what's asked of you. So even if you're assigned a task that is, indeed, not your job, refrain from saying so. Instead, try to find out why your boss is assigning you this task--there may be a valid reason. If you believe that doing the task is a bad idea, you can try explaining why and suggesting how it could be better done by someone else. This may work, depending on the boss. In any case, remember that doing what's asked of you, even tasks outside your job description, is good karma.
"It's not my problem." When people say something is not their problem it makes them look like they don't care. This does not endear them to anybody, especially the boss. If a problem is brewing and you have nothing constructive to say, it's better to say nothing at all. Even better is to pitch in and try to help. Because, ultimately, a problem in the workplace is everyone's problem. We're all in it together.
"It's not my fault." Yet another four words to be avoided. Human nature is weird. Claiming that something is not our fault often has the result of making people suspect it is. Besides, what's the real issue here? It's that something went wrong and needs to be fixed. That's what people should be thinking about--not who is to blame.
"I can only do one thing at a time." News flash: Complaining you are overworked will not make your boss feel sorry for you or go easier on you. Instead, a boss will think: (1) you resent your job, and/or (2) you aren't up to your job. Everybody, especially nowadays, feels pressured and overworked.
"I am way overqualified for this job." Hey, maybe you are. But the fact is, this is the job you have. You agreed to take it on and, while you may now regret that decision, it's still your job. Complaining that it's beneath you only makes you look bad. Plus, coworkers doing similar jobs may resent and dislike you.
"This job is easy! Anyone could do it!" Maybe what you're trying to convey here is that you're so brilliant your work is easy. Unfortunately, it comes off sounding more like, "This work is stupid." Bosses don't like hearing that any work is stupid. Nor do they really like hearing that a job is easy peasy. It belittles the whole enterprise. If a task is simple, be glad and do it as quickly as you can. Even "stupid" work needs to get done.
"It can't be done." Saying something can't be done is like waving a red flag in a boss's eyes. Even if the thing being suggested truly is impossible, saying it is can make you look ineffectual or incapable. Better to play detective. Why is the boss asking you to do whatever it is? What's the problem that needs to be solved? What's the goal? Search for doable ways of solving that problem or reaching that goal. That's what bosses really want. Most of them do not expect the impossible.
Last words: When in doubt, remember that silence really is golden.