Two and a Half Men, Season 3

Alan:
Uh, well... uh, uh, you see Jake, um... In the Old West, uh, uh... cowboys, uh, could be out on the-- the dusty range... uh, uh, for months... at a time, and, uh, they get mighty dirty. Um, so they'd, uh, they'd, uh, mosey into town, uh, with nothing but the-- the clothes on their backs, uh, and th-- they'd need to, to, to wash them. So what-- what they'd do is, uh, they-- they would go down to the-- the, the... "crick", uh, and, uh, strip down until they were wearing, uh, nothing but their boots.

Charlie:
Why'd they keep their boots on?

Alan:
Rattlesnakes. [to Jake]: Uh, anyway, um, in order to... to, to warn, uh, people who were swimming that, you know, a-- a naked... cowboy was, uh, on his way, he would yell, or, uh, or, if you will, uh, call, uh, "Booty! Booty!" Ergo, the "booty call".

Kandi:
Wow. Alan, you really make history fun.

Alan:
Well, thank you.

Kandi:
So when did it start meaning casual sex?