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 popular Nintendo game,
Animal Crossing.
Tanner: So what are you trying to do here?
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.
Reil: But I jumped the turtles last week...