When Emmett and Paden ride into a town, Hobart, who's leading a group of settlers, mistakes them for two guides he and the other settlers have hired:
Hobart: Baxter! Hawley! Where the hell've you been? You're late and I tell you, I don't like it. It's a bad start, boys. I got my people down there throwin' snowballs and rarin' to go.
Emmett: I'm afraid it is a bad start, friend, cause my name ain't Baxter, and he ain't Hawley.
Hobart: You're not Baxter?
Emmett: Name's Emmett.
Hobart: You're not Baxter either?
Paden: No, I'm not Hawley.
When Baxter and Hawley end up robbing the settlers of their money for their boss Dawson, Emmett rides into their hideout with his "dead" partner (Paden) and pretends to be on the run from a posse; does Dawson mind he crashed here?
Dawson: Mind? You bring a posse to my best hideout and you ask me if I mind?
It's James Gammons' delivery of the line that really makes it funny.
Later in that same scene, Emmett tries to "help" by getting the horses, while Mal, as part of the "posse", starts shooting in his direction. True to form, he only "misses" by a couple of inches, and after one shot, Emmett turns around and gives him a look as if to say, "You don't have to make it look that good!"
Cleese gets several, from the way he shuts down the racist bartender to his casual final "Pick up my hat" after it's shot off his head.