Apparently pressing C-[ (three times in a row it seems?) (or alternatively ESC three times) closes a frame. I oftentimes accidentally press C-[ when I meant to press C-p. I tried to disable it with
(define-key "\C-[" KEY nil) which does nothing
as well as
(dolist (key '("\C-["))
(global-unset-key key))
which for some reason makes my meta key not work anymore.
How can I disable \C-[?