Originally Posted by mvnsnd

Over the yellow is just bad form and should be called out. As far as going to the front on hills, as long as it doesn't interfere with the group dynamic, it's Ok. If they get to the hill and then block others progress up, that's also bad. On a hammer ride, let him go. If their time at the front is only these occasions, then again, not good. The behavior should not disrupt the point of the group ride.

It really is a group dynamic thing. If the group is Ok with it, then fine. If his behavior is a safety issue, then it's not fine.