If you sense that you are making someone uncomfortable give them an out. Say "I would like to talk but I see that you are busy, I don't want to distract you from your work." this gives them an opportunity to either respond with, "no, you're not distracting me at all" or "thank you, I'd rather be left alone" note: if you are a woman it helps to err on the side of less friendly the first time you meet someone, women who are too friendly are usually assumed to be looking for sex, when talking to men, unless they are very old ladies.