South Park Season 5 Episode 9

Kyle: Remember when life used to be simple and cool?
Cartman: Not really.
Butters: (walks to the bus stop) Uh, hey. How's it going fellas?
Stan: Butters! What the hell do you think you're doing??
Butters: Well, I'm just standing around being a kid, why? How come you're wearing them oogy spaceman masks?
Kyle: These are gas masks, Butters!
Stan: Yeah, if you don't wear a gas mask, you'll be easily exposed to smallpox or anthrax!
Butters: What?! Oh, Jesus! I don't wanna get the 'thrax, fellas! W-what do I do??
Stan: There's nothing you can do…except stop breathing.
Butters: Stop breathing??
Kyle: Yeah, you can't get it if you don't breath.
Butters: Oh, all right, then! (inhales deeply and holds breath)