What is a good temperature to set your air conditioning to when it's really hot out?

If you want to keep it at the temperature setting that your roommate has it, consider getting a fan for your own room. It actually keeps the air circulating better and keeps things cooler. Cool air settles down near the floor, using a room fan circulates it up and around the room, making it cooler and more comfortable. Let her/him roast, you don't have to. You'll be cool as a cucumber. We use a fan at night in our bedroom and in the living room in the daytime. Our AC stays at or around 75 degrees.