If you ever watched the show "Perfect Strangers," it involved two cousins, one a urban man named Larry, and the other, a foreigner named Balki.
Larry was the kind of guy who was always trying to take the easy way out, to say stuff like "but EVERYbody does it, so it's okay!" and always trying to take short cuts and never wanting to own up to his mistakes.
Balki, though, was the innocent and he always had to be Cousin Larry's conscience.
Therefore, when used in reference to discussing comics, a "Cousin Larry trick" is when a creator does something sneaky (I first used underhanded here, but that has too much of a negative connotation), most notably the use of "irony in afterthought."
The term comes from Mike Nelson's review of "Wild Things," and his example of a Cousin Larry trick is the specific example that I personally use most of the time, and that is that the producers of Wild Things set out to make a thriller, and when people mocked it for being a poor thriller, they attempted to claim that it wasn't a bad thriller, but a good comedy.
That's a Cousin Larry trick.
And you'll see it used in comics a lot.
Chuck Austen is currently using a Cousin Larry trick with his independent series, Worldwatch. It is terrible exploitative comics with awful dialogue and characterization, but if you point that out, you're told "it's SUPPOSED to be like that!"
Total Cousin Larry trick.