To accidentally excrete poo from one's anus into one's pants, generally due to copious amounts of alcohol consumption wherein all bowel control has been lost.
"Oh man... I got SO drunk the other night at this party, I Vanced everywhere... I had to remove my Vance pants and walk home in the nude".
"Hurry up in the bathroom dude!! I'm gonna Vance if you take any longer in there".
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