Old western duals were at high noon so neither person would have the sun in their eyes.

[at the town festival] Buford "Mad Dog" Tannen: Then let's finish it, right now! Buford's Gang Member #1: Uh, not now, Buford. Uh, Marshal's got our guns. Buford "Mad Dog" Tannen: Like I said, we'll finish this tomorrow. Buford's Gang Member #2: Tomorrow, we're robbin' the Pine City Stage. Buford "Mad Dog" Tannen: What about Monday? Are we doin' anything Monday? Buford's Gang Member #1: Uh, no, Monday'd be fine. You can kill him on Monday. Buford "Mad Dog" Tannen: I'll be back this way on Monday! We'll settle this then... right there... out in the street... in front of the Palace Saloon! Marty McFly: Yeah, right. When? High noon? Buford "Mad Dog" Tannen: Noon? I do my killin' before breakfast! Seven o'clock! Marty McFly: Eight o'clock. I do my killin' after breakfast!

/r/Showerthoughts Thread