What about someone shitting in your mouth?
Licking [and even worse sticking your tongue right in] man anus I find is always a low point, but its becoming more and more common.
Just generally being degraded. Like they fuck you then leave you naked on the front door, on the street corner etc. Though most of those are probably not real.
I once saw a crazy Jap video where they abuse this Jap girl on a train, then when they get to the station she's naked, and they push her out. She's all smiling and laughing til the train pulls away and she's still standing on the platform totally naked.
I can probably think of a few more.
I mean just when you think porn can't go any lower, 50 guys pummeling some poor whores are, pissing on her etc, along comes donkey punch.