When someone says something so outrageous and unbelievable, one may say "Are you out of your tree?" which means that the person is out of their mind on such an idea. The phrase originates from the popularNintendo game, Animal Crossing.
Reil: I'm going to jump that shark tank on this here bike.
Tanner: Oh no, no, no! Are you out of your tree?! You can't hope to jump something like that on that thing. You may as well start jumping turtles before doing something so unbelievable.