Oh-oh, he might be catching on.

Yesterday, we had this conversation.

Elijah (holding his toy dump truck): "fffffff-uck".
Me (cringing): "No, no, T-ruck.  Teeeee-ruck".
Elijah (giving me a sly look): "fffffffff-uck".
Me: "No! Teeeee-ruck!"

Elijah(with sly look turning to sly joy): "Fffff-uck teee-ruck!!"
and, before I can say anything else, he looks triumphant, throws up his hand and says:
"Ha! HIGH FIVE!!"
... and he high-fives me.  He looks very proud of himself.

I folded over laughing.  I couldn't help it.
So there you have it.  Not only does he say it, he now clearly gets that it sort of gets a rise out of people. Great. HIGH FIVE, Mom! Awesome job.