Dude, do not bring home a pet without asking
Sure, they can be cute to look at, but pets are a huge responsibility (and burden if your roommate didn’t want one in the first place). Soon there’s cat fur all over the place, your roommate’s sneezing every five minutes, and @ShelbytheSiamese -- who’s still not Instagram-famous like you had hoped -- has marked her territory in every corner of the room.
Don’t leave the trash can full after you dump all your garbage in it
You’ve both got to do your part to keep the room neat and not smelling like a landfill. If you decide to throw out every half-eaten, moldy piece of yuck/blech/ew from the fridge, don’t leave that mess for your roommate to smell and/or dispose of later.
It’s not cool to never, ever leave your room
It’s awesome that you feel safe and comfortable in your first away-from-home living situation (we’ve been there; the unfamiliar can definitely be a little scary), but no need to turn your dorm room into a full-fledged bunker. Get out there and smell the fresh air so your roomie can get some privacy occasionally.