A nonexistent girlfriend (not that internet service schtick). I have one of these. The pros far outway the cons. No dates to remember, no birthdays, so you can basically be a slob and get away with it. If you give her some interesting problems, she'll really be 3 dimensional. Mine's a kleptomaniac and a narcissist.
Mom: Where are all your pens?
Me: Bonnie must have stolen them.
Mom: Who the hell's Bonnie?