A phrase originated by Miss Alli of Television Without Pity, a website devoted to television shows. The phrase is used to combat a reality show contestant who feels the need to pray to god to help them get through their task or win the game. God does not stop to interfere with reality shows and you should think of him as in the tub. Like when you're a kid and you're mom is in the tub, you should let her enjoy her alone time. She should not be bothered. God is in the tub.
Just jump off the cliff already and stop praying. God is in the tub.