The letter reprinted at Blue Jeans Cable Strikes Back – Response to Monster Cable makes for some fun reading.
Here's how it starts,
RE: Your letter, received April Fools' Day
Dear Monster Lawyers,
Let me begin by stating, without equivocation, that I have no interest whatsoever in infringing upon any intellectual property belonging to Monster Cable. Indeed, the less my customers think my products resemble Monster's, in form or in function, the better.
I'm not a patent lawyer, but the trademark and trade dress parts of this letter look pretty good to me, and the patent stuff was fun to read — seven words I never wrote in that particular order before. I even laughed.
(Thanks to OJ for the link.)