When a girl's ass transforms into a largemass and volume within a very short period of time less than 12 months similar to the immediate U.S. land expanison of 1803.
Dan: Dude, I don't know how her ass got that big. It was small last year.
David: Yeah, it was, that's a total Lousiana Purchase.
The act of soaking a rubberband in lousiana hot sauce, then while hittin it from the back, stretch aforementioned rubberband as far as you can and take aim at your unsuspecting partners pooper. Let 'er rip and try to hold on!