Useless boast of the day:

[kentauros]

"I am mythological."

[Dr. Strange]

1. No you're not.

That's a myth.

[kentauros]

2. I did say it was a useless boast, right?

Seems I fulfilled the parameters of my OP :P

So, what's your useless boast? ;)

[Dr. Strange]

3. My useless boast is the S. S. Minnow.

No, wait, that's my useless boat.

My useless boast is that I know all of the words to the song YYZ.

[kentauros]

4. I don't know the song, so you have me there

But you might like a thread in GD that makes excessive use of the letter Z. Just look for the one with "UGA student" in the title :D