They bring in a suspect who really dislikes Benson and Stabler. So they put Munch in! One comment about Newt Gringrich's lesbian sister, and BAM! Munch is off on a political rant.
Outside, Cragen shuts off the audio in the interrogation room. "Anybody know where Cassidy is?"
"I'm in the middle of rehersal here!"
"And we're in the middle of a homicide investigation."