A sexual act, with twins, one of which is sitting on your face while you are eating her out. While this is going on the other twin is riding your dick and of course the twins are making out with each other completing the Pertwindif triangle of enjoyment. There are multiple variations of this sexual act such as the blumpkin-pertwindif or the cosby sweater-pertwindif.
Dude i'm going to pertwindif the shit out of the those twins. Literally.