Gotcha. Is it a new usage? I wouldn't say my british slang stays super up to date necessarily... maybe I forgot this one, but I don't remember seeing/hearing it in the past.
Australian here, heard it all my life. Also, in our dialect you can use fuck to mean pretty much anything, as long as it's clear from context what sentiment you're going for
In America, "piss off" can mean "leave", but "pissed off" means angry (usually, depending on context it can also mean left). "fuck off" means "leave", while "fucked off" either means "left" or "screwed around". It's complicated haha. In this post, I guess "fucked off" could've meant "left" too, but that reads very awkwardly to me so I decided against that theory. Then others are telling me it can mean angry, or least I'm taking their responses to mean that, so I'm thinking OOP meant that here. But maybe I'm still confused! /shrug