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.
Zara: Lol.
Mark: You fucking what?
Iain: I love Lauren.
Mark: Fuck off Iain.
A colourful practice that has increasingly common during Zoom calls in the pandemic. Some people find it helps to relieve their lockdown stress, and take solace in the freedoms that would get them fired under normal circumstances.