That’s the punch line, sampled by The Beastie Boys from a comedy album by the late, great Mantan Moreland.
What’s the joke/full text of the story?
Here’s the full bit.
That’s awesome. 
Is that true that fuck means to serve in French?
No. Fuck is an English word. It doesn’t exist in French. The closest phonetical equivalent would probably be “phoque” which means “seal” (as in the animal).
Besides, if I remember the joke correctly the mademoiselle was asking what F U C K meant in English, wasn’t she ?
If this is gonna be that kind of thread, I’m gonna put a seal in the mashed potatoes. Aark aark!
That’s how it is in friedo’s link. Parce que je ne parle pas français, I don’t know if there is a phrase that phonetically would be written F U C K in English. (I doubt it.) So I interpreted it as someone having written some graffiti on the board and the teacher lied rather than to be embarrassed by using a vulgar word. Or it could be that ‘to service’ would be close.
Reminded me of this joke:
A man decides to have a party and invites lots of people, telling them to bring their friends. On the invitation he puts “Theme Party Come as a Human Emotion.”
On the night of the party, the first guest arrives and he opens the door to see a guy covered in green paint with the letters N and V painted on his chest. He says to this guy, “Wow, great outfit, what emotion have you come as?” and the guy says, “I’m green with envy.” The host replies, “Brilliant, come on in and have a drink.”
A few minutes later the next guest arrives and the host opens the door to see a woman covered in a pink body stocking with a feather boa wrapped around her most intimate parts. He says to this woman, “Wow, great outfit, what emotion have you come as?” And she replies, “I’m tickled pink.” The host says, “I love it, come on in and join the party.”
A couple of minutes later the doorbell goes for the third time, and the host opens the door to see two blokes from Jamaica, stark naked, one with his penis stuck in a bowl of custard and the other with his penis stuck in a pear.
The host is really shocked and says, “What the hell are you doing? You could get arrested for standing like that out here in the street. What emotion is this supposed to be?” The first guy replies, “Well, I’m fucking disgusted, and my friend here has come in despair.”
Or is this joke what the OP was talking about?
I heard it "“Well, I’m fucking disgusted, and my friend is deep in despair.”