When the lobster from Claws! tricks Johnny into believing he has won the lottery, Johnny mentions he has never won anything before in his life. This is untrue however, as in the first season episode Over the Hump he won the "Find the Fort" competition together with Lawrence the Camel.
He has also won a luxury cruise (but ended up on a pirate ship) in Moby Jerk.
As a side note, the check for the fake lottery the lobster was holding refers to Johnny Bravo as "Johnny Q. Chump".