dude, just act like it's fine for now and be nice to her and whatever, then wait until she marries someone and they settle down and then when they decide to start a family wait until they have their first born child then wait even longer, until it's like 4 or 5 and they've become very attached to it and figure out what park the kid plays at and when they aren't looking take the kid and run! Then hold it for ransom and use those creepy ransom letters with the letters cut out of magazines and shit and demand they give you at least like $50,000 for their kid back then they'll give you $50,000 and you can leave the kid under a bridge somewhere...
or you could just find a new girl...