When I lived with my parents, I'd hotbox the bathroom. I'd bring in the TV and laptop and some video games, a friend and I would order some pizza and smoke a few blunts and play Super Smash brothers. Sometimes we'd smoke a hookah too.

Sounds like a strange thing to do, but the smell's easy to get rid of if there's a fan in the room (most bathrooms have one), and it's small.

In dorms, we've covered a a bunkbed in blankets and sheets and weighed them down so that it was pretty thoroughly covered. The bed was placed against a window, so we'd be able to sit in there, smoke for a few hours, and then open the window before we got out and let all the smoke out. A girl once stopped by our room to see what was going on while we were doing this, and apparently no smoke let out, but we looked funny and the whole hall reeked.