Never had a bad encounter with a CM at the parks...but I've seen others have 'em. Bottom line seems to be follow the rules, don't be a jerk and you'll find most CMs are great. Sure they're must be some that are having a bad day or just flat out not up to Disney par but I've yet to encounter one.
Worst experiences I've ever had with "CMs" have been here at MC. But that's cool, everyone needs to vent about their job.