The joke is that it could mean both,
"joke" may be putting it a bit to strongly.
(PsychoChomp, Fri 8 May 2009, 12:18, archived)

I GET THIS JOKE.
Aha.
( Dr Preference AjcuiVd289, Fri 8 May 2009, 12:28, archived)

That's because you've got a advanced sense of humour.

(PsychoChomp, Fri 8 May 2009, 12:30, archived)

I also got several extra layers of meaning that even you didn't know were in there.

( Dr Preference AjcuiVd289, Fri 8 May 2009, 12:31, archived)

It's amazing how much funny I can jam "between the lines"

(PsychoChomp, Fri 8 May 2009, 12:31, archived)