Please don't correct me, it sickens me.

I had not one but two people come up to me at the Y today and correct my form. Maybe I'm just extra tired today. I had an easier time listening to the one guy because he was frickin huge. I'll take his advice and do smith machine shoulder presses instead of regular shoulder presses. Ouch. Very ouch. The other was on calf raises. My back it seems is getting all the work on those exercises. How come my back never hurts but my shoulders and calves do?