off one's rocker

to be off one’s rocker/trolley - свихнуться, слететь с катушек

off your rocker (INFORMAL) (CALD)
If you say that someone is off their rocker, you mean that they are behaving in a very strange or foolish way.

off your trolley (UK INFORMAL) (CALD)
behaving in an extremely unusual way or doing something very silly:

Anyone who saw us doing this would think we were off our trolleys.
Have you gone completely off your trolley? You'll never get away with it!

be off your trolley (humorous) (CDI)

to be crazy
What are you doing eating chocolate and cheese again? You're off your trolley!