Better yet, intimidate them into moving out!

I had a craigslist weirdo roommate once. He seemed like he'd be great--grad student, really concerned about peace and quiet, etc. Moved in and started messing with my shit in careless ways (fucked up my cast iron pan, etc.), made vague threats about not paying his half of the first internet bill ("there are some... there are some charges on here I'd like some time to review carefully first"), et cetera. One morning, I come out from taking a shower wearing my usual pair of athletic shorts or whatever, and walk into the kitchen to pour myself a glass of orange juice. He's in there making breakfast. "Halfascientist," he says, "seems like you, uhh, really like walking around here without a shirt on." I set down my glass and stare at him, wordless. "Seems like you like it or something. Like you're gay or something." I cough out a mouthful of juice, laughing, and remain wordless. "I think that's pretty disgusting of you, you know, to walk around like that." Jesus, dude... weren't you from Portland? I walk out laughing.

Three days later I set him down on the couch with the internet bill and say, "you've already bought this. Now all you have to do is pay for it. Which you'll do. Now. Or I'm changing the password. You are no longer to use any of my things--my knives, my pots and pans, et cetera. And I won't be responding positively to any suggestions or requests for me to put a shirt on in this, my own house. Because I live here. And if I want to walk around with my dick hanging out, I will do so. If any of this sounds incompatible with your lifestyle, maybe it's best that we make a clean break, and you start looking for places right now."

He and his stupid acoustic guitar and moldy homebrewing equipment were gone in a week.