I’m so old I remember when peace was invented, so I may be off base, but I think they get it from hip-hop videos. Not sure what it’s supposed to mean, though — and I probably don’t want to know.
Yeah, it’s hip-hop, “peace out” or can mean I am carrying a firearm. Sometimes it is across the chest, so, in summation; THP was correct, it means: I am a dumbass. :)