What to do when you meet someone you already don't like?

We all have a couple people that we know about, or have heard about but haven’t officially met yet. Let’s say that person is someone that you already don’t like and have a negative association with before ever having shook hands.

What do you do when you finally meet that person? To give some context, what if it’s in a social setting with mutual friends/girlfriend etc. Do you do the professional thing and shake hands when you’re introduced? I’ve always been curious about what others would do in this situation