To lay the smackdown on someone, to annihilatethem or to win an argument or fight with ease.
Man 1: 'Dude, this girl Nicola, she came at me all like, "dick, why you been acting so fucked towards me?"'
Man 2: 'Damn, what did you do?'
Man 1: 'I laid The Smackdown on that fuckin' bitch!'
Man 2: 'Word.'