I like the guy who comes screaming down the MUP straightaway at > 25mph approaching a group of slow walkers some pushing baby strollers --and proceeds to holler obscenities at everyone for being in his way as he buzzes within inches of them. (observed on the fox river trial west of chicago)

On the other hand, I've been on a deserted remote pea-gravel MUP trail making some good time myself when I see ahead of me two bikers laying down (including bikes) in the middle of the path sun bathing.

Brain not required.