I find the pack riders are the worst. They think if there’s enough of them together then the world should stop for them. When I cycle I do it on my own.
Actually this is a common issue. It is one reason I tend to ride alone
The lone riders may be the worst. About once a week I have to dodge one on one of the roads I used to commute. The road is clearly not built for bikes on the street, and I have looked at the “bike routes” for the town and it is listed as not for biking on the street. But they still do it, and clog up traffic right at the light.
After a couple of blocks - oh, I am not supposed to be on the road - and they get onto the nice wide sidewalk.