In my book, that dubious distinction belongs to the Julia Roberts/Natalie Portman/Clive Owen/Jude Law psychodrama Closer. The movie isn't gross like Antichrist, or menacing like The Comfort of Strangers, and no one gets raped. But the movie is deeply cynical about love—each character uses romantic connection as fuel for his or her ego. Fans of Pretty Woman or even Erin Brockovich might have gone to see the film because it starred Julia Roberts. They were expecting the toothy grin of America's sweetheart and the happy ending that usually follows her around. But in Closer, Roberts and her dashing lovers (Owen and Law) are selfish and manipulative. It's an alienating viewing experience, one that diffuses, rather than facilitates, romantic connection.That is a bad one to be sure. But I think there are worse ones. Generally, I think horror movies are bad date movies because I'm a wuss and I don't want to jump/hide/scream/cry in front of a date. The worst horror movies, though, are ones where a seemingly normal (and often very attractive) woman turns out to be the monster.
Species is one of the classics of this sub-genre. Nothing ruins a date more than the suspicion that any amorous activity might end in the removal of your spine through your mouth.