A 'better' alternative to using the word 'crazy' or 'insane' to someone. Or just a fun way to call someone crazy. Also, 'mentally jolly' can be used. From the Family Guy episode 'The Fat Guy Strangler'.
"Dr, is my brother really insane?"
"Mrs Griffin, we don't use the word 'insane', we prefer the term 'mentally hilarious'"
The way far too many people spell "hilarious." It is definitely one of the most popular misspelled words in the english laguage. "Halarious" is how most people pronounce "Hilarious" in every day speech. This is the root of the word.