I don't think I've ever enjoyed "CSI: Crime Scene Investigation" more than the first half of Thursday night's episode, scripted by the writers of the CBS comedy "Two and a Half Men."

I wrote last week about the writers of "Two and a Half Men" and "CSI" trading writing assignments for an episode. Monday's "Two and a Half Men" was OK, but the comedy went down better in the drama than the drama did in the comedy.

"Men" writer Chuck Lorre worked on "Roseanne" and "Cybill" and it's clear he brought his experiences to bear on this script, which begins as knowing fun but veers off into unrestrained Chucklesville before the end.

Annabelle (Katey Sagal) is the nutjob sitcom star who treats her writers and co-star terribly. Rachael Harris plays the co-star Megan Kupowski, which sounds a good bit like "Cybill" co-star Christine Baranski.

Like Roseanne, Annabelle has a dim-witted former bartender boyfriend from middle America (clearly a gloss on Tom Arnold).

All the roman-a-clef stuff works great, but then the bad jokes begin. When the CSI team suspects a writer was hiding in a closet, Nick (George Eads) says, "Looks like a comedy writer came out of the closet."

"I doubt if it's the first time," Catherine (Marg Helgenberger)chimes in.

There are references to "Two and a Half Men" (and a blinked-and-you-missed-it cameo by the show's stars), "Valerie's Family" and a bizarre bit with a mime.

And then there are the puns:

"A mime is a terrible thing to waste."

"What we have here is a failure to coagulate."

"So the clot doesn't thicken but the plot does."

It all began as a successful trade, but by the second half of this week's "CSI," the episode veered wildly off course. Oh well, it was still a fun experiement to watch Lorre exorcise his sitcom diva demons.