Runaway Jury and Elephant both have killing-spree scenes (at a law firm and a school, respectively), so that could put people on edge a bit. 
Pretty much any hard-R or X-rated movie could make it an office party to remember!
Blazing Saddles
&
Schindler’s List
Oh, and “Natural Born Killers” is probably not work appropriate on a number of levels too.
Tough nut to crack . . . I can’t think of any film that would be particularly disturbing to people in the IT business or in the consulting/outsourcing biz . . .
Since “outsourcing” is sometimes a synonym/euphemism for “getting fired,” how about Fun With Dick and Jane?
Nudge nudge… there’s more than one of these.
Lots of good ones. I’ve added a number to my rental list. Some, I think, I will avoid, though.
Others that come to mind:
A History of Violence
Team America: World Police
Pink Flamingos (1972)
Fear & Loathing In Las Vegas.
I commend to you “How To Get Ahead In Advertising” a simply spiffing movie which is absolutely perfect to watch with cow-orks! Heck, large segments of it are all about work…
I’m surprised nobody’s mentioned THE BROWN BUNNY.
I personally like this movie, but many people think it’s the worst film ever made. You be the judge.
Young Adam
Pet Sematary
Schindler’s List
Flowers in the Attic
Caligula
Naked Lunch (anything by Cronenberg would do, really, but this is my #1 recommendation. Nothing says “work party” like talking anuses! Good times.)
Last Tango in Paris
Trainspotting
Believe it or not, it has been done. A friend who works at Lucent once had a department outing scheduled to see the stage play, until management realized that it was, ah . . . somewhat out of step with contemporary business norms.
For a sales department, you can’t go wrong with Glengarry Glen Ross.
I actually showed it about a decade ago at a chuch singles gathering. No, I was not driven from that church. Yes, any film recommendations by me are still viewed with suspicion.
Especially popular with the gals in the Typing Pool!
Aww, someone already picked Requiem for a Dream and Doom Generation. I think the follow up to DG, Nowhere might be a better choice, though. I mean, DG doesn’t have aliens, and aren’t aliens something that reminds you of coworkers more than garden shear mutilations do?
Anyway, I’m going to suggest Wicked instead. You could play it off as “I haven’t heard much about this independent film, but I know it took a while to find someone to distribute it on DVD. Probably because Julia Stiles wasn’t well known yet.” 
I specialize in inappropriate movies.
I vote for Alucarda. Wildly over the top Mexican horror movie about nuns who worship Satan and then flip out and go on a killing spree. Kinda. There’s a satanic goat orgy, screaming, lesbians, screaming, lots of burning and carnage and screaming and a literal blood bath. Good clean fun. Your coworkers will love you for it.
I’ve reduced an entire room of people to a fetal position with this film.
Another choice would be Robo Vampire, but I think your coworkers might stab you to death for that.
Pretty much anything with a description that includes any of the following words…
“gory”
any-“fest”
“bukkake”
“hentai”
should clear a room of co-workers in no time. :eek:
I’ll just tell 'em I thought it was a version of the broadway musical.
This reminds me, about 10 years ago I had a Lynch-o-Rama party with showings of Blue Velvet and Eraserhead. It was a very exclusive guest list.
How about Demonlover, a mainstream French film about a large corporation that apparently does major real estate deals but plans to REALLY make money distributing adult Japanese cartoons, and also has an adult website somehow related to the management. It features Jennifer Tilly and Chloe Sevigny and is not porn, but it is VERY silly – but not intentionally so.