To not do something previously agreed to. (usually at the last minute)
Can be shorted to 'gas out'.

Or to reject an idea/suggestion.
Example A;

Person A: "hey man, ready to go?, it's gonna be awesome!"

Person B: "...errrrm... actually i think i'm gonna gas it out.

Person A: "You're an idiot."


Example B;

"I was going to see my bird last night but i thought i'd gas out and have a pot noodle and a wank instead"
by moon boy October 23, 2008
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