I think a guy would think negative thoughts if a girl where to paint her whole face in class lol but just doing something simple like lipgloss catches the attention of some, more so if he likes you. But never curl your eye lashes in front of a man...never!
"Why is she putting gunk on her face in the middle of everyone, during class. Can't she wait till class s over, & do it in private.. Probably looking for attention. I guess she's not a conscientious listener.. and not very attentive. She probably has a very short attention span.. Talking to her would be very dull"
There could be diffrent things he is thinking about, like he likes how you put it on or it's jut very amusing to him or he could just like you. But in a relationship it's diffrent. some guys like looking at their girls putting it on.
Most men complain about how girls wear make up, but if she feels confident in it, you should be happy for her. I do understand that a lot of make up is way over the top, but some girls use it to express them selves, when they don't know another way to do it.