Have you ever noticed that when you are unexpectedly asked for your name you usually say "Uhhh
"I'm Tom by the way, what's your name?"
"Uhh... Derek, aka the person who's house you are currently in?" Make sure to give him a look that says "dumbass"
Typically they respond along similiar lines of "Oh damn! I didn't know! My bad bro!"
Also don't be concerned with facts. As long as the guy/girl doesn't live at the house themselves this will work.
As always if you want to tell me how stupid this way or that I suck leave a comment below or follow me on twitter @DeRexBowles where I will make your eyes bleed with my inner most thoughts and feelings.