When someone is in the wrong, or someone " tries" you (makes you out to be stupid), it is time to shut them down. For instance, when someone tries to talk to your boyfriend/girlfriend then it's time to shut it down. Meaning, stopping the whole situation permanently.
alicia: girl.! i heard ricky cheated on cece AGAIN last night.! i hope she okay.
boonetta: girl you already know cece went in there and shut it down. ricky know what the deal is now.