To finger another person; to have sexual intercourse.
"Yeah i got with her and wet some knuckle"
when a man or a woman is sitting on the toilet and they start to finger there asshole and they dip there knuckles in the toilet bowl water
"what took so long in the bathroom?"
"I was about half a finger in and I had to stop"
"why? you get wet knuckles?"
"yea"