Yep, I like Nny.
I feel unqualified to describe it in depth, having only read it and Squee for the first time about two months ago. But...
JTHM is a seven-issue comic by Jhonen Vasquez, the guy responsible for the Invader Zim cartoon. Well, mostly responsible... just like Ren & Stimpy before it, Nickelodeon screwed around a lot with the finished product. But that's neither here nor there.
Johnny is a serial killer, and he wastes anyone who slightly pisses him off, whether it's somene who laughed at his hair, or the guy who turned off the slurpee machine at the convenience store. He also hallucinates extended conversations with a pair of styrofoam doughboys, and a dead rabbit nailed to the wall (and later, just its floating severed head).
A comic about a murderer doesn't really seem like the best source of comedy, but the book really is funny, and toward the later part of the series, it shifts away somewhat from the bloodspray. You can get it and Squee (which collects many of the incidental JTHM stories) in GN form, and I recommend it.