The phrase 'slag off' is used in many ways, meaning somebody has been talking about you badly to another person
Jenny was slagging you off yesterday, she said you were ugly. She slag off me all the time
To verbally attack, using disparaging terms.
He.was.slag.ging.me.off.in.the.bar.so.I.beat.him.and.fucked.his.bitch.har.har.har.
YEAH YEAH YEAH
Another term for "shut the fuck up" or "shut your fuckung mouth".
Jack was boulshitting all the day, so I asked him to slag off.
A term used to explain when someone is talking behind someone's/your back.
I heard Emily slagging off Connie earlier.
A person insulting you or another.
Slagged = insulted
Dave slagged me off behind my back
Originates from Essex meaning when someone is chatting shit about you behind your back and obviously you confront them about it saying:
Person 1- apparently you've been slagging off jasmine
Person 2- says who? I can promise you now I ain't said one word about the girl.