Similar to a wet willy except that instead of licking your finger to get it wet, you stick it in a woman's vagina to get your finger lubricated. Then you stick your finger in her ear like a wet willy.
I was rolling around naked with my girlfriend, and then all of a sudden she said she didn't feel like having sex. I was pissed, so I stuck my finger in her coochie and quickly gave her a wet vagilly to teach her a lesson.
A Wet Vagilly is similar to a Wet Willy, except that instead of using saliva to lubricate the finger before it goes into someone's ear, the finger is wet with vaginal lubrication. Vagilly is a portmanteau of the words "Vagina" and "Willy."
Aaron: If you don't get out of bed, I'm going to give you a Wet Willy!
Trina: You better not, if you do, I'm going to give you a Wet Vagilly, and you don't want that, because I'm very aroused right now.
Aaron: Ok, you win...that's nasty.