To start a fight.
When I called them wankers they started kicking off.
When a person acts in a belligerent manner, usually as a result of excessive alcohol consumption, although it is possible to 'kick off' whilst sober.
Zara: Have you seen Mark?
Sam: I think he's in the lower Pollet kicking off.
Mark: You fucking what?
Iain: I love Lauren.
Mark: Fuck off Iain.