Don’t say: “That’s not my job.”
Why: If your superior asks you to do something, it is your job.
Instead say: “I’m not sure that should be my priority right now.” Then have a conversation with your boss about your responsibilities.

Don’t say: “This might sound stupid, but…”
Why: Never undermine your ideas by prefacing your remarks with wishy-washy language.
Instead say: What’s on your mind. It reinforces your credibility to present your ideas with confidence.

Don’t say: “I don’t have time to talk to you.”
Why: It’s plain rude, in person or on the phone.
Instead say: “I’m just finishing something up right now. Can I come by when I’m done?” Graciously explain why you can’t talk now, and suggest catching up at an appointed time later. Let phone calls go to voice mail until you can give callers your undivided attention.

Expert: Suzanne Bates, president and chief executive officer of Bates Communications, an executive-training firm in Wellesley, Massachusetts, and author of Speak Like a CEO (McGraw-Hill, $22, amazon.com).

Source: http://www.realsimple.com/work-life/etiquette/sticky-situations/common-phrases-avoid-conversation-10000001698308/page2.html