Guys who grab for other guys privates out in public view of others, why?

When I was in elementary school some of the guys would grab for the other guys crotch, nobody in particular, just any crotch they could get close to. I always quickly swung my hand down and blocked them, or sidestepped them. This happened out on the playground where anybody could have seen it, including the girls or the teachers. Years later I worked in a big city factory where 2 of my male coworkers had the same custom of grabbing for other guys crotches, although I never saw them grab each other. This was quite annoying to me, and when I told them to knock it off they would just laugh. One day when I was particularly irritated and one of these guys did that to me I told him that if he would go brush his teeth I would let him give me a blojob. After that he left me alone. I've never encountered that custom anywhere else in my entire life, and I still wonder...what did it mean??

Was this a form of sex play? Were they hitting on me? Or did it have nothing to do with sex? Maybe it was a type of bullying, or whatever?? Anybody have some insight on this issue? Any of you ever do this to people? If so, what did you mean by it. Did any of you ever experience this and come up with an effective deterrent?