chocolate thumb

To chocolate thumb someone is to place your hand in the 'thumb up' position and rest it on a seat next to you so that when a person sits down your thumb goes up their anus.

Penatration of the anus is unlikely when the victim is fully clothed, however not impossible.

when all fingers are clasped together, this leaves both thumbs together in an upright position. Insert the thumbs into your partners rectum, pull them out. Insert your penis into the rectum, reach around and stick your thumbs in their mouth to be sucked.