Vacilão in this context would mean more like "dumb-ass" or "moron"

But the translation is correct, to vacilar is to falter, but this is more like a slang use of the word.

Btw this was a case where a dude got caught stealing something (can't remember what), the guy who caught him happened to be a tattoo artist, so they actually tattooed that to his forehead kek.