I used to love aerobics (well, still do, I just never go to classes anymore), especially the classes led by this one, very fit, very energetic, bouncy woman with terrific dance moves and a great sense of humour. But she'd walk around and SCREEEEAM at us to get us to work harder, and she'd "cheat" on the counting when we were doing say, sit-ups (i.e. "Eight to go! Six! Four! Four! Four! etc.). I'd be going 110 % all the time anyway, and pacing myself carefully to last for those final counts and I swear, at times I just wanted to reach up and smack her 
But I digress. I'd prefer being told why doing x is wrong, and then being allowed to choose for myself. Unless I'm doing something harmful, of course, or truly don't notice what I'm doing wrong.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett