Short for Fuck You and See You Tomorrow.
Based on a meme that circulated in the raging, divisive pandemic days of 2020 that showed a cranky, old geezer stepping out a door. It was labelled "When you and your friends have different political views but you love them the same. Fuck you and I'll see you tomorrow!"
Used to remind someone that though they are a fuck head, you're putting up with them. Mostly used endearingly, especially when used by Canadians toward Americans.
What kind of moron does says something like that? Well, FUSYT.
You're wrong. FUSYT.
I gotta go. FUSYT.