Sleaziest films of all time?

Last House on the Left. "Piss your pants!"

I don't think that just because a film takes place within "sleazy" environments, that the film itself is sleazy. Most of the films in your list have great (read:powerful) intentions/messages and therefor are hardly exploitative. Paul Shrader is no idiot (Taxi Driver, Hardcore, and Auto Focus) and I highly doubt his intentions were to titillate. As far as his American Gigolo goes--that is exploitative but too dumb to leave me with the unclean feeling that sleazy films usually accomplish. I just got done watching Hardcore and that one is full of style lest one thinks that style negates sleaze. In addition, the film is quite deep in it's (Shrader's)faith and you can learn a lot about the dutch religion if you pay attention. Just compare it to 8mm which is crass and just plain stupid(not to mention a complete rip-off). I think it's the "movie" ending to Hardcore that sadly lessens it's impact. If it had been filmed as intended, with the girl dying in a totally unrelated car accident, than it's message may have lingered a little longer. That being that some individuals can be saved while others are destined to destruction. Cruising is definetly sleazy because it's highly exploitative and extremely exaggerated in it's depiction of the gay lifestyle. Of the films you listed, The Exterminator is sleazy. Night of the Juggler, maybe. Straw Dogs is too powerful to be considered sleazy. If that's sleazy just because of rape, then is Tess sleazy? Extremities? In the Realm of the Senses is an Art House staple which is hardly the outlet for sleaze. Alien? I'm going to pretend I didn't read that. And to put The Elephant Man in the same list as The Exterminator and Cruising seems totally ridiculous. Patch Adams, yes. But not the sweet story of John Merrick. To me, it all depends on the intention of the director. If the film was made to get people off (wether it be via sex or violence), then yes, that is sleazy. I would say, for my money's worth, some of those titles would be:

Maniac
Combat Shock
Last House on the Left
House of Whipcord
House on the edge of the Park
Don't go in the House (nor the basement for that matter)
8mm (this film is totally tasteless--style or no style)
Angel (though it does have 'heart' when it comes to her street friends)
The Killing Hour
He Knows You're Alone
Mother's Day
Pieces
Island of Death
Cannibal Holocaust

The Dark Backwards is by far the sleaziest movie I have ever seen. I'm not even sure what to think about that movie, but it defintely brings the sleaze.

Also, the rap group ICP (Insane Clown Posse) did a movie called Big Money Hustlas (or something like that). I couldn't take more than about 20 minutes of it, but it was definitely sleazy.

Let us not forget Henry: Portrait of a Serial Killer

When it comes to sleazy movies, nothing tops Hard (1998) and Locked Up (2004).

I found these films to be incredibly trashy and a visual shot of penetration short of being porn.

My vote would be for "Hated", a short documentary about punk rocker G.G. Allin, shortly before he died. It's actually very similar to "This Is Spinal Tap"., but it's all real. It contains both hilarious and gross scenes.

I'd like to add:
Toys Are Not For Children
Don't Answer The Phone
Mondo Trasho
Multiple Maniacs

"Don't Go In The House". That is one movie in which is definently not recommended for normal people, about a guy who sets women on fire.