Is it normal that my friend is obsessed with drawing penises?

so ok I have a friend that's obsess with drawing penises he has a girl tho we go to college together and we sit together and he draws penises on my note book when I'm not looking if ask him if he was gay he's just says nah I'm just playing bro on a rainy day he drew a penis on a window I mean I thought it was funny but Now it's just plain annoying and I told him to stop it's getting old and he still keeps drawing penises on my notebook just yesterday when I was presenting a project and came back he drew a whole chain of penises around my note notebook i mean WTF? he's cool and all but he won't stop. Doing that shit what should I do? Is he gay?