I think the worst reaction I've seen is this look that says "You poor thing." I feel like people don't take me seriously when I stutter. I used to get made fun of in school too, but at least adults aren't that dickish about it usually. It's that look that I get that kills me. And frankly, very few people (at least where I live) want to associate with someone that takes 30 seconds to say "Hi". It makes them feel uncomfortable, even if they know they can't make fun of it.