Let's say you're talking to some casual acquaintance and they do something that you don't like... and it's enough that you'll actually avoid them whenever you reasonably can from that point on. What did they do?
My answers are:
1.) Touch me.
2.) Flirt with or hit on me.
More so the latter. There aren't many other things that people can say to get me to not want to talk to them anymore.
edit: the worst possible thing someone could do is tickle me... even someone I'm attracted to