I went on a group ride once and one of the guys on the ride leaned on the car at a stoplight. The driver didn't say anything, but several other riders told the guy not to do that. The guy tried to justify it by saying "What? I wasn't going to damage the car, I was just touching it!" Then we all started to scold him until he finally unclipped and took his hand off the car. For the next mile or so, several riders told him in no uncertain terms, "If you want to ride like a jerk, find another group." He never showed up again.