Unless you're at a Mexican-themed party or a southwestern-style restaurant, or actually in Mexico, you can usually trace back and identify the moment the tequila came out as the point at which the evening spun seriously out of control.
Nobody ever says, "Yeah, you know, we're just going to have a quiet night in, drink a little tequila, maybe get a movie or something." Never in the history of the world have those words been uttered seriously.
My theory is this: The world is divided into those who adore tequila and those who cannot see how, once upon a time, somebody sipped some agave juice that had been sitting out for a while and thought, "Ay! This stuff is pretty good! We should bottle it and sell it to gringos!" By the time the tequila comes out at the party, everyone is usually willing to drink it. The male hormonal imperative to prove masculinity by drinking nasty things is in full sway over half the assembled company. The female social imperative to lose control and do really silly things is running the show for the other half.
When people are acting that way, is it any wonder madness inevitably ensues?