Source: http://www.mit.edu/~tahnan/ling-humor.html
(I've changed the order around just a little. The comments are from the original page, not me.)

Miscellaneous Linguist Humor

A linguist practical joke
An incredibly geeky phone prank which you can only get if you studied a little syntax. (If you haven't, ignore it or play along.)
Call the Gap. When the salesperson answers, ask them, "Hi, is Tracy there?" They will presumably tell you that there is no Tracy working at the store. Say, "What, no Trace?" When they say no, yell, "Hah! No Trace in the Gap! Chomsky was wrong!" and hang up.
(OK, it's not a very good prank.)

A joke (not original to these pages, but worth repeating)
You've probably seen how various professions prove that all odd numbers above 1 are prime.

(If not, it runs like this:
The mathematician says, "3 is prime, 5 is prime, 7 is prime--by induction, all odd numbers are prime!"
The physicist says, "3 is prime, 5 is prime, 7 is prime, 9 is, um, experimental error, 11 is prime, 13 is prime--looks good."
The engineer says, "3 is prime, 5 is prime, 7 is prime, 9 is prime, 11 is prime..."
And the computer scientist writes a program which prints out, "3 is prime, 3 is prime, 3 is prime...")

So how does a phonologist prove that all odd numbers are prime? "Well, 3 is prime; 5 is prime; 7 is prime. 9 doesn't look prime, but if we say it isn't we're missing an underlying generalization here."

And the GB syntactician? "3 is prime. Therefore, all odd numbers are prime."

A random linguistic Tom Swifty
"It's the down-carat semantic operator," Tom said intentionally.

Linguist poetry

Double Dactyls were invented by Anthony Hecht and Paul Pascal. The basic rules, and some rather nice examples, can be found on Raphael Carter's Double Dactyl page and in Alex Chaffee's Double Dactyl collection. They're somewhere between limericks and sonnets in terms of restrictiveness, but resemble limericks in their obligatory but catchy rhythm and their typically whimsical nature.

X-sub-i, Y-sub-i
Polly I. Jacobson
Brown U.'s semanticist
Uses CG;

"What does it mean to say
'Coindexational'?
I think that things should be
Variable-free."

Higglety Pigglety
Mark Johnson, Ph.D.
Speaks in a dialect
Missing the r's.

Slash-categorical
Work becomes difficult:
Since you don't know if you
"Pass" it...or "parse."

(A note to the reader: Mark Johnson's Australian accent makes it such that both quoted words in the final line of the second double-dactyl are pronounced pretty close to identically--"pahz," more or less.)

Santa Cruz Santa Cruz
William A. Ladusaw
Understands negatives
Better than me.

I'd say there ain't never
Been no one half so good
Writing on negative
Polarity.

Another dreadful linguistic pun

The LSA encourages linguists to use example sentences that do not include such violent (but clearly transitive) verbs as "kill" or "hit." Therefore, if one is discussing the diagnostics for the covert element PRO, one should avoid using a sentence such as

John wants [PRO to be killed]
but instead to use sentences like
John wants [PRO to be arrested]

While the LSA's guidelines are fairly recent, there is a sense in which this harkens back to the sixties, when this sort of thing was fairly common--that is, being arrested as part of a non-violent PRO-test.