I found one of the french movies I was thinking of, it's called "Romance". I saw it on the culture channel once, I had no clue what it was about, I was sitting on my couch and thought I was going to enjoy my artsy, highbrow french movie and...BAM...next thing you know is you see a close up of a gynecological examination at an university with a couple of medicine students...all lined up to ram their fingers into the female lead character's vagina. There were a couple of hardcore oral scene's too. Keep in mind that this is a sophisticated mainstream movie and the actress is a serious performer, there was nothing pornographic or tasteless about this film (it was rather touching)...just it featured real action. It's said that this is the first mainstream movie to show an errect penis.
That's the one that came to mind as well. They were only supposed to go so far but both got really into it & the scene was too intense to just stop so they let them keep going...
If you've seen 9 Songs, you'll definitely agree that the sex was very real... I mean, it's basically an arty porn film... There's no clever editing or anything, you pretty much see EVERYTHING. Was weird seeing that bloke from Childrens Hospital as the main character getting his rocks off for real right in front of your eyes though...