it can mean two different thing:
dude: Fuck you you're so annoying
or
dude: ill Fuck you
Used for when teachers are spying on you through their new internet software and think it's okay.
Student 1:"Oh damn the teachers are spying on us." Student 2: "Fuck you teachers!"
A good way of telling your parents that you have great grades in school, make sure you say that parent's name after, it will make them completely speechless!
(don't blame me for any injuries that happen afterwards)
Dad: Hey Son, How are your grades?
Son: Fuck You, Dad!
Dad: ...