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.