Even though I use 'mad' with the other meanings on here, I can't believe I haven't seen THIS yet. 'Mad' in Australian culture also means something like 'freaking awesome'.
'If only she dyed her hair purple instead, she would've looked so mad.'
A term used by psychotic governments to describe a fact that they can make sure that everyone will be DESTROYED in a Mutual Nuclear Exchange, no matter who fires first, IE an Atomic War. WAR IS MAD. This made the term First Strikeunnecessary.
The USA and China both have Atomic Bombs so that they can stay MAD.
The Soviet Union used to be able to get MAD, but now they just sell the ability for others to get MAD.