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1.
The area in your head where thoughts of a single person constantly reside.

When a person online has annoyed you so much or out argued you so much that you constantly think about them and how to insult them again and again, and you constantly post about them, then they have occupied your crawlspace, similar to that small area under a house, they have moved in and taken up residence in your brain causing you to think about them all the time.
Message board post #1: SPEMike is a cockhomo fat-ass who can't get a girl

Message board response to #1: SPEMike is totally in your crawlspace dude.

by SpofoAnon June 09, 2007
 
3.
a rather large vagina.
I was fucking this chick and her vagina was so big it was like a crawlspace. I needed a headlamp to find my way out.
by Hemie the Clown August 03, 2010
 
4.
n. The last place you'll never see.
A woman's throat in the hands is worth three in the crawlspace.
by captain cracklins September 25, 2003