davearonson said about 6 years ago on Random Ruby Tips and Tricks :

Be careful when using ||= with Boolean values.  ||= will set something not only if it's nil, but also if it's literally false, i.e., the one object named false, of class FalseClass.  In short it will set it if it's "falsey".

That part also reminded me of some strange code I encountered recently: "if status == status = 1 || status = 2 || status = 3".  See http://blog.codosaur.us/2016/11/x-x-wtf.html for a writeup of what that was probably meant to do, and what it really did.