Not in jest, not halfway playing around, not behind their back. Just “fuck you” or a close variation like “go fuck yourself”.
And what caused you to say such a vile thing to your fellow human being?
Never. Just not my style. Although I don’t consider it a particularly “vile thing”.
I don’t actually consider it especially vile either. But personally I don’t say it except in extreme circumstances. I know people who will say it at the drop of a hat. I’ve said it to maybe two people ever.
I’ve never said it to anyone either. I guess that means I’m either very non-confrontational or I’m just a sissy. 
Out loud or in my head?
Out loud, a long time ago, if ever. In my head…
I said “Shut the fuck up” to my cousin in a facebook comment, in response to a crass political remark he made after I expressed sorrow at the Newtown shooting. He totally deserved it, and we’re still friends.
I try to avoid such expressions.
However, if you were asking when was the last time someone told me to f off, well I get that all the time, in so many words or less. 
Been years since I said it for real. I have friends who I will say it to if they are busting my stones.
The last time I said it was quite a long time ago, in the middle of 11th grade economics to some jerk named Paul. I yelled it at him quite low, right in the middle of class and we were more or less across the room from each other. I remember thinking I had finally pushed too far with my devil-may-care attitude when the whole room got silent and the teacher stared at me. But then I looked at him, said I’m sorry (the teacher, not to Paul) and he never said a word.
My expletives tend towards cursing rather than profanity, so I am far more likely to damn someone than to tell them to fuck off.
Apparently I am a lot more profane than the rest of youse. Actually as I get older I find that I kind of enjoy the looks I get when I curse or flip the bird. I guess gray-haired wrinkled old ladies aren’t supposed to do that shit.
It was about 13 years ago. I was on a large organized bicycle ride with my daughter and we caught a guy messing with the road markings in such a way that he got dozens of people severely lost. I wanted to beat the crap out of him, but wanted him to take the first swing. Actually I said a LOT more than FU to the jerk. In fact my daughter, who was 14 YO at the time, said that she had heard all those words, but not in those combinations. Fortunately for both of us, the jerk got in his vehicle and drove off.
I think the F-bomb, and many other choice 4-letter words, are overused and seldom say them myself. However if I do, people listen.
Yesterday. A couple of colleagues and I were driving back to the office from lunch when I thought a car was going to pull out in front of me, so I slowed down to let them in. They didn’t go, so I gradually started speeding up again. Suddenly an SUV is honking from behind me, whips up beside me yelling something (his window was closed), then speeds up and whips in front of me. I was so surprised by his sudden outburst of anger that my colleagues and me busted out laughing at the guy. About then he sees us and rolls down his window and yells “FUCK YOU!!!” We go to the next light right as it’s turning red; but he runs it anyway :rolleyes:". I turn left and go back to work.
Wow, I totally misread that. Hmm, I don’t know the last time I said it with seriousness. I do have a potty mouth so I’m sure I’ve said it to friends and such.
Never.
Never. If I’m arguing with someone and they say it, I figure they couldn’t think of an intelligent response to my last point. Therefore, I won.
Never. I would say “go fuck yourself” or “I don’t give a fuck”, sometimes “I don’t give a flying fuck” because alliteration is fun.
In desperation I said it to a boyfriend once in the middle of a heated argument, probably eight or nine years ago. The expression was attended by me emphatically pointing at him so that he could be clear that the “you” in “Fuck you” was indeed HIM as he lounged on my bed like a total douche.
The contorted look on his face was so worth it that I’m sitting here smiling as I type this.
Last time I said it so that the target could hear, maybe last summer. It is always in traffic, so they can only hear me when the windows are down. Last summer though, it was face-to-face through the car windows after a woman drove me off the road merging into my lane. She apparently felt I hadn’t gotten out of her way fast enough so she stopped long enough to lay a “fuck you” on me. I almost used the C word too but it doesn’t come naturally to me so I missed my chance.
I’m not positive it was the last time I said it to someone, but I said it to my *mom *about 15 years ago (when I was in my early 20s).
She was nagging at me about my boyfriend at the time, and I was sick of her talking at me, and it came out of nowhere. I just wanted her to shut up. I think I even asked her a couple of times to leave me alone, to stop talking to me. Finally, a big “Fuck you!” and we were both shocked into silence.
IIRC, she did shut up and we never mentioned it again. I think it’s the first time anyone had ever said that to her. I don’t regret it one bit – she needed to hear it.