1 Samuel 21:12-15

When David realized that he had been recognized, he panicked, fearing the worst from Achish, king of Gath. So right there, while they were looking at him, he pretended to go crazy, pounding his head on the city gate and foaming at the mouth, spit dripping from his beard. Achish took one look at him and said to his servants, “Can’t you see he’s crazy? Why did you let him in here? Don’t you think I have enough crazy people to put up with as it is without adding another? Get him out of here!”