"The Joker Gets a Royal Flush" from The Joker #5 (DC, 1976) by Martin Pasko, Irv Novick and Ted Blaisdell
In the mid-70s, DC started publishing a bunch of crazy high-concept books, only to cancel them before they reached the 12-issue mark. Of these, two villains got their own books. There was Kobra (still to come) and there was the Joker. More a merry prankster in this series than a psychopath, the Clown Prince of Crime got to go up against many thematically-linked opponents, from the Creeper (who stole his laughing shtick) to the Royal Flush Gang (get it?). It was nothing like The Killing Joke and it lasted only 9 issues.