To orally lubricate one's own finger with saliva and insert into another person's anus. Similar to a Wet Willy, but in the B-hole.
Rob gave Scott a Wet Billy.
by MTOny March 9, 2021
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Wet Billy is when you kick you're finger and shove it up someone's ass.
Person 1 . Man we we're having sex and she gave me a wet billy!
Person 2 . Wet Billy?
Person 1. Yeah she shoved her slobber fingers up my asss
by Robietommyson September 22, 2022
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