Never really happens in any group that I am in. Larger groups tend to roll around and actual speeds go up and down with the terrain. I have noticed that a few people seem to fall off when speeds go up without any real increase in effort (because slight decline or tailwind) which is weird. Equally you get the people who sit on the front and then stop pedalling downhill...actually quite annoying. I rarely see anybody trying to deliberately drop anyone (except on the big climbs, which is fair enough). Also there are always a few shepherds (me included) who keep an eye out and drop back and pace people back or stop the group. But, there are riders who are utterly oblivious to anyone else and smash on, never looking back at all. One of the things I really like about the club is that there isn't an annoying patriarchal figure barking orders, and there are enough experienced and strong riders to silently determine pace and do the little jobs to keep things cohesive without making a show of it. There was a self-appointed patrician, Gerald, late 60s, who would stake out his authoratitive position by telling you at every opportunity that he used to race, as if that was somehow relevant, but he left after he mansplained once too often to a couple of women and got his comeuppance.
The small groups of faster riders is where the real naughty fun is, and people will launch an attack, often with a huge grin, and then get dragged back by a paceline with counter-attack. We all know each other very well and none of it is about ego. It's just pissing around having a blast. It all works quite well really.