Bruno Kirby (Ed Furillo) was extremely allergic to horses. Prior to each day of filming, he required an injection of allergy medication to get through the day.
Now that's true dedication.
Jack Palance as Curly and Duke equals total ownage!
Phil beating the crap of the Jerkass cowboys put in charge after Curly had died, and making one of them think he's about to shoot him.
Phil: I'm not going to let them bully us anymore!...My father-in-law was a bully!...I hate bullies! Because bullies don't just bully you, they take away your dignity!
Not exactly in the movie itself, but when Jack Palance won the Best Supporting Actor Oscar, he started doing one armed pushups on stage, at age 73, mind you.
Mitch finally standing up to Curly - "If you're gonna kill me, then do it. If not, shut the hell up. I'M ON VACATION."- and finally earning the cowboy's respect.
Mitch, Ed, and Phil bringing in the herd, singing the theme to Bonanza.
Curly's Establishing Character Moment where he teaches the two cowhands who had been sexually harassing Bonny and about to start a fight with Mitch and company a little respect, including when he he throws a knife at the crotch of one and it comes within inches of hitting the guy right in the crotch.
City Slickers II
Mitch rescuing Glen just before he and the wagon he's in goes over the nearby cliff. Mitch even lampshades it.
Glen: (freaks out when he spots Mitch) Wah! What are you doing?!