What the fuck is this? Is u75 so full of bosses, managers and allied bastards that it functions as an advice-giving branch of the CBI or Institute of Directors?
I don't claim that it is never right to sack people, but without knowing why the worker called the manager a fucking cunt and a fucking arsehole and seemed aggressive, I cannot possibly say the worker was in the wrong. Without further information, I'd give the worker the benefit of the doubt, not the manager.
And maybe the manager is a fucking arsehole.