I wonder if this isn't a side effect of our moving to be a "less violent" society. Back in the day, that person would at least get punched for doing such a thing, and would not do it again. As it is, there's really no negative reinforcement to such actions, and so they don't see the point of not doing them.
No need to start punching. Just confront them on their behaviour. 90% of the time they'll back down if you call them out. They're just school-bullies grown up.
