rusty dunk 

Act of sticking ones finger in ones rectum, at minimum two knuckles:
proceeding to dunk or stir said finger in the drink of an aquaintance.
Can be used on friends, enemies, or even family as well.

That fat ass doesn't know i rusty dunked his cloudy limon earlier at the bar.

rusty dunk by Rexual B. January 6, 2009