Actually, I think this was an anthology movie (but I can't be sure) and this was just ONE story of it.
Anyway, a nerdy college guy puts up an advertisement for a roommate, and this guy answers it. The guy (I'll call him Bully, cause that's what he is) starts immediately intimidating the Nerd Boy and just being an overall bad roommate. He demands all Nerd Boys furniture be put in HIS room, claiming the ad said the room was "furnished", leaves a huge mess and dinner and just overall makes his life hell.
At one point Bully has his girlfriend and laster, when Bully leaves, Nerdy Boy talks to her, and notices a tattoo she has that reads, "Satan's Slut." Later (not sure how) Nerd Boy is at the morgue when they find a mutilated body and recognizing the tattoo on the corpses stomach-it's Bully's girlfriend. So Nerd Boy is pretty sure Bully killed his GF and starts spying on him.
Now, I missed a bit of the film, so when I turned back, Nerd Boy is in the hospital injured is on a respirator (not sure how that happened) and no one but he knows that Bully is a bad guy. Bully comes to visit, taunts Nerdy Boy, who then tries to strangle Bully, but, lacking the strength, dies instead.
Nerd Boy's mom comes in and, seeing that Bully was the last guy to see Nerd Boy alive, asks if he said anything. Bully replies, "He said he loved you. And he told me make sure I get my safety deposit back."
The movie (or segment) ends with another Nerdy, wimpy looking guy putting up a notice on a board and we see Bully looking on, obviously scouting his next victim.