When a person changes their accent for the purposes of swearing, usually in an unsuccessful attempt to make them sound cooler than they actually are.
Keiran: Did you bring the cards?
Keiran: Christ man, I teld you ta bring the cerds, it's fucking borin' without them.
Brian: Stop talking like that, you're aren't Begbie from Trainspotting.
Keiran: But that's my swearcent!