Alan, Charlie and others in “Ergo, The Booty Call”

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.

Why'd they keep their boots on?

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".

Wow. Alan, you really make history fun.

Well, thank you.

So when did it start meaning casual sex?