Yeah, Happiness would be up there, but the first that would come to mind (because it was actually a date film for me) would be Lilya 4 Ever.

If you watch Happiness on a date, the other person will most likely think you have mental issues.

Come and see

I actually saw Happiness on a first date.

OMG.
Salo.
Yes, that would be far worse.
At least you could debate what this film means afterwards. With
Salo,
you'd just be stuck sharing a barf bag.
.

I'm surprised nobody's mentioned Salo yetor Cannibal Holocaustor anything by Jodorowsky!

The Human Centipede
could be a real killjoy (!)
(Before the sequel came out which I skipped, thank you very much people were posting about what could happen in it. I said the Centipede should go out on a job search, and hit the dating scene. I would like to see it handle the classic office disaster scene where a Xerox machine goes crazy and starts spitting papers everywhere. I think I suggested the sequel end with the centipede dressing all in black, and trying to pull off a diamond heist or something in the dark.)
.

I saw that with a migraine, and with my then girlfriend. We argued on the ride home, and shortly afterwards I broke up with her. Good times!

I agree with all these suggestions. I recently had a girl over on a first date and she was all "lets watch silence of the lambs!!" little did i know she was this innocent mormon girl who rarely watches R films.
So we watched it. and it creeped the hell out of her. its been over two months now and i haven't heard or seen her since.
but whatever.
Boogie Nights would make an interesting first date movie lol

Same good choices already names, I'll add Requiem for a Dream to it. It's one of those movies that can ruin your whole night and make you feel miserable.

I nominate
Meet the Feebles
as the worst date film.
http://7capitalfilms.blogspot.com/

Nekromantik.

AntiChrist and Irreversible came to mind first. Also Martyrs, Audition and The Girl Next Door.

Anit-Christ by Von Trier has explicit male and female genital mutilation
Dictated, but not read.

6. KIDS
   Don't watch the movie KIDS on a date unless you plan on being celibate for a long time.
7. Seven is a pretty rough date movie as well

My first thought for a worse date movie was Irreversible.

Are you implying that young girls would like to be called Bob?

Oh, I know a few girls who would like this.

I concur, there is something strange about adults calling a young child bob. Must be a polish thing