The person who is in charge/in command.
Usually one would say this to assert themselves as a leader or
Ask this aloud to question the competency of the person in charge.
(1) Bloke 1: "I reckon we should do it this way"
Bloke 2: "Well I’m fucking this chook mate, so shut the fuck up. We're doing it my way"
(2) A bloke after waiting for food for a long time in terrible restaurant stands up angrily and yells "Who’s fucking this chook?!? Where’s my fucking food?!?"