Meaning, "I dislike you strongly," in intelligent language. Used in these situations, not in particular order.
1. Heated argument
2. Child sticking their tongue out (means "fuck you" in toddler")
3. Used when friends embarrass you and you have nothing to say against it
4. When your iPod, computer, or other device freezes up unexpectedly.
You: AWWW, what an adorablelittle dimpled child you have!! (Condescendingly)
A double definition word Fuck you either means to express your hate for someone using profanity or, to want to engage in sexul intercoarse with someone