Symphony in SLANG (1951, dir. by Tex Avery)
The cat has always been my favorite part. :p
Done as a one-shot, with all original characters who never appeared in any other MGM cartoon, Symphony is pretty much an anomaly in Avery's canon. What makes it even more so is the fact that Avery hired designer Tom Oreb to design all the characters and layout for the entire film. Just for this one cartoon. That's it.
Oreb had been working at Disney pretty consistantly at the time, but left the company in the early-50's. Oreb worked with Avery at MGM for this one cartoon and then went back to Disney where he designed characters for such projects as Toot, Whistle, Plunk & Boom, Sleeping Beauty and One Hundred and One Dalmations.