How do you say ' are you sane'?
I was viewing the 'all for laughs' video compilations, the scenes were really funny. In a lot of them, people would goggle at the pranksters with surprised or suspicious faces and point their index fingers at their own temples ( not expressing with words for politeness) when they were witnessing the pranksters' crazy or foolish behaviors (for example, eating the soup-artificial- inspite the bird-droppings just fell in ).
1) what would you say at the pranksters behaviors to mean ' are you insane'? What's the common expressions? And are there some idioms or slangs?
In a video experiment (in the US or Canada), a white man were saying' nickel, nickel' or some other words including 'nickel' when they are passing by or were near black people, and immediately the blacks would get outraged and began to beat him.
2) why blcaks would get angry at people saying 'nickel'?