Basically the same meaning as cap ( which means lying) but it is used more commonly as sarcasm or as a joke.
Guy 1: I don't know what On god means.
Guy 2 : hahaha that's w cap.
1👍 1👎
W-Willie-Cap is a word you will use after you successfully spread misinformation and get your friends or peers to believe it,
"Dude did you hear he's dating a skinny chick?" "WHAT?! No way I could've sworn he only liked fat girls" "Hahaha gotcha bro that was W-Willie-cap