A bar prank where someone takes 2 open Corona or Dos Equis bottles, shoves them upside-down in the pockets of an unwitting victim, and immediately assumes the stance of an Old West gunfighter in a standoff. The victim will inevitably turn around and yank the pouring bottles, like a pair of six-shooters, out the pockets of his/her now-drenched pants, at which point the prankster will then mimic triumphantly shooting the victim with their finger pistols. This works best on a timid-looking victim who probably doesn't have a large group of drunken, belligerent friends around.
Mexican Gunslinger in action:
Prankster - "Bartender, dos cervezas, por favor."
*SHAKE SHAKE SHAKE* <shoves in victim's pockets>
Victim - "Dude! What the fuck!?" <yanks out bottles>
Prankster - "GUNSLINGER! PEW! PEW! PEW!"