fucked up shit. used to describe a moment or event of any sort.
you are masturbating is your room. someone walks in. you do not have enough time to hide your stuff and pretend you were not. this is a F.U.S. moment
you and your lover were making out. a few school children walk by. you stop back up and pretend to be checking you cell phone. they walk by knowing exactly what was up. this is a F.U.S. moment.