During Season 1 of High Stakes Poker, Doyle Brunson ran a failed bluff against his friend, Ted Forrest. After he was caught, Brunson was heard mumbling to himself “I know better than to bluff an idiot.”
Brunson obviously does not believe that Forrest is bad at poker — rather, he was just humorously lamenting his bluff getting called. In spite of this, many people took his words completely out of context. They use them as a mantra to remind themselves not to try and bluff players in small stakes games which they view as a sea of idiocy teeming with schools of fish incapable of folding.