I think there's a whole different set of skills and judgments for riding on MUPS. It's not as obvious as riding in traffic or road races, but just as real nonetheless. I have to say that the roadies, the roadies with enough time in the saddle to be pretty fast, are generally the most skilled and safest on the MUPS from what I've seen. Until they get in groups but that's a different story ... I've seen OP's situation a lot of times and I agree that those guys are accidents waiting to happen but just as often from the slower guys. The roadies mainly just misjudge my speed coming at them but I usually feel pretty safe with the close maneuvers with them unless someone panics. The real skill, in my opinion, is seeing in advance where that sort of thing is possible and avoiding it before it starts.