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'"
When a person laughs hard enough they pull both wrists to their chest and open their mouth while rocking back and fourth but stay in their own personal space. Similar to a velocilaughter.
Adjective: description of any expression, statement or definition which, although originally intended in earnest, results adversely in humorous disdain.
"Wendy's attempt to explain how her underwear ended up in the frat house rec room was unintentionally hilarious."