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1.
when your ass starts hurting because you have been sitting down on a long trip
I got buttlag after two hundred miles.
by Brian Smith November 08, 2004
 
2.
When you buttocks is stuck to the leathery office chair, after a long night of gaming, creating a butt lag.
Ow! that was some serious butt lag.
by brocklie January 16, 2009