Usumacinta Special
The act of preparing a nice big fresh bowl of home made guacamole, freezing it in the shape of a butt plug, putting the frozen guac-buttplug into your partner's ass, waiting for it to start to un-freeze and then fucking them in the ass. The result is often a brownish green mess that resembles the Usumacinta river in southeastern Mexico.
Dude I gave my girlfriend a Usumacinta Special last night. She really enjoyed, but was not happy with the mess it made. I don't think we will be eating tacos for a long time now.