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1.
The only answer to the question Why.

No matter what you say, you can always ask why. The only way to end it is by saying Why Not.

Saying why after why not just doesn't make any sense!
-I like Urban Dictionary
-Why?
-Because it's a great website.
-Why?
-Well, for one it allows me to define words.
-Why?
-Cause that's the whole damn point of the site!
-Why?
-Why not?
-...
by ? January 02, 2005
103 15
 
2.
A phrase used amongst a group of men (friends to be exact) while agreeing that they'd "hit it". Typically used while the opposite sex is in close proximity as an effort to be discreet.
Ted- "Damn... You see that chick over there at Forever 21?!?"

Tyrone- "Shiiiiit... Why not!"
by L-dub123 October 10, 2013
8 0
 
3.
A reason/excuse given by people to do anything at all. Because of its universal nature, this is often used as an excuse to do something stupid.

Not to be confused with the Pokémon Wynaut.
Why not go rob that bank over there?
by GuardianSong August 07, 2012
7 3
 
4.
Other way to say ok.
Let´s watch a movie this night ? of course, why not ?
by edgnets December 11, 2007
7 3