It wasn't COPS; most episodes of COPS are three 7-minute chapters, if you will, while the "pizza chase" scene took less than 2 minutes. It was an episode on one or more of those police pursuit/chase shows currently on Spike and/or TruTV (nee Court TV).
FWIW, I did not find the pizza chase "hilarious" in any way, shape, or form, as it was potentially dangerous for all involved (i.e., what if the pizza guy accidentally (or purposely) hit the perp or, worse, the cop? what if it had turned out that the "perp" was actually an undercover cop running away to make it "look" good to watching drug dealers or similar? That's why cops don't like it when people get involved in such a way; that it had a good result is not the issue). Perhaps one needs to be drunk when watching it (just don't drive, afterwards, or you'll be the one being chased by the pizza guy on the next COPS episode!) 
Coincidentally, COPS' new season starts tonight: Sept 12, 2009!
Edited on 09/13/2009 12:33am
Edited 7 total times.