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1.
Equivalent to "go ahead".
If you need to leave, go for it.
by Albert February 15, 2004
 
2.
A term used by guys (usually of the unpopular and geeky teenager type) when there is at least one girl in the room.

The statement is relatively cryptic. It is often assumed to be a shortening of one saying "Go ask that girl out." However the exact girl to be asked out usually is a mystery and the meaning can be interpreted in different ways.
Christopher, Jack and Tim were sitting at a table at school. In the same room were a few other girls. Suddenly Christopher smirks and says to Tim "Go For It." Tim then replies back "Go For It" giving Christopher a taste of his own medicine. Jack meanwhile sits amused watching the two but finally can no longer resist the urge he has and says "Go For It" himself.
by akabugeyes May 03, 2008