If I do its just foundation and mascara and chap stick. Anything else would melt off and that's really gross looking! Plus we get a natural flush of pink in our cheeks and lips from exercise. So things like blush and lipstick/gloss are things you can skip when going to the gym. You will generate your own natural glow! :) I also barely sweat from my face so I don't have to worry to much about my make up looking nasty.
I think the idea of a girl putting on makeup to go to the gym is absolutely retarded. It's pointless and shows she's not going to actually work out but to troll for guys. The only exception is when a girl is coming to the gym from work or some other place they had to put on makeup for, so they already had it on.
Never. I'm working out, I have no use for it. I mean if I don't wear much in the first place why put it on when I'll just be sweating? It's tacky when girls do it. Are they really that low in confidence they have to wear makeup to the gym?! I see it way too often. I go to the gym for me, so I can feel good after my workouts and during, not to try and be pretty for whoever's around me.
I usually go to the gym in the afternoon or early evening after I've already been in school/work/etc and when I go out I generally wear makeup anyway, so my makeup is just on anyway, but not because of the gym.
If I'm just going to the gym straight from home I probably won't put it on just for that, though sometimes I'm just in the mood to wear makeup because I have fun applying it.