By starting a communication with "Fuck you!" you do several important things.
1. You show that you are authentic and will say and do whatever you think. No pretending or fake tolerance.
2. You check how intelligent and mature a person is. If it is a problem and it offends them, there would be no honest communication anyway. People that can be offended by that will be offended by many other things. You decide if you want to waste your time.
3. Show your level of playfulness. Humor is the basis of intelligent communication.