Decide to Rise Above It
Dealing with a bad roommate can easily become a power struggle mired with pettiness, antagonism and immaturity. This is unnecessary and will pay you much more to make a decision to rise above it all and refrain from resorting to passive-aggressive vengeful behaviour. Try to dismiss it as the irrelevance that it is and refuse to fall to the level of pettiness it would take to maintain a struggle with your bad roommate.
Talk To Them
Many times rather than calmly speaking to our roommates about the things they do that get on our nerves, we are passively aggressive, caustic and rudely direct towards them. This should not be. First appeal to your roommate's sense of reason by calmly approaching him/her and starting a conversation, and then be willing to compromise and find a middle ground between your needs and theirs.
Ignore Them
If you're not going to be in the situation (that is, be his/her roommate) for long, make a decision to ignore them. Just let it go and avoid him/her as much as you can until it's over and you no longer have to be stuck with him/her again.
Talk to the Staff or Landlord
You can always complain to the staff (house mistress, caretaker etc.) or landlord about the excesses of your roommate. The staff or landlord might be more effective in finding a solution to the problem because many times, the staff or landlord has had to deal with similar situations in the past.
