If you enjoyed Seitokai Yakuindomo (that perverted first thing we watched), then brace yourselves.
I've found something worse.
Mind you, it's not hentai. But this is about as close as you can get to crossing the line.
It's called Hen Zemi. Watch it at your own risk. You can view it in its purest form here: http://www.animetake.com/hen-zemi-episode-1/
Don't say I didn't warn you.
Oh yeah, I should also mention that it employs some gross-out tactics as well. To be expected of course.