Knucklebutting

The act of inserting multiple fingers at least second knuckle deep into your partners rectum, optimally by surprise. Often done during fellatio or cunnilingus.

Sabrina is great at knucklebutting, she can get third knuckle deep before you even notice.

Knucklebutting by SasquatchSB October 5, 2010

Knuckledusting 

When a loved one or significant other won't help a bro out and he's forced to knuckle his own junk. Said bro shoots baby batter into his own hand and allows it to dry. The following morning punches the unwillingly participant from the night before creating an eruption of cum dust shooting from his knuckles.

Liz wouldn't go down on mike, so he gave her a full-on knuckledusting the next morning.

Knuckledusting by Georgiamrlory July 20, 2010