What should I do about wanting to make monkey noises and imitations whenever I see a dude under 5'9?
Are you trying to offend them or something?
Most of my 'cool' friends with their high GPAs will make fun of them
You're going to be an ass to strangers to impress your buddies? You need to grow up and leave people alone about things they can't change.
No one is making me do it.
That's the point, no one is making you do it. So your choosing to be rude and disrespectful to strangers just to entertain yourself and and your friends. Instead, you should do the right thing and show everyone the same respect that you want to see.