I'm a mean motherfucker when it comes to farts. I love leaving "presents" in elevators. Once did it, and some folks got on with a baby, and they thought the kid had just shit it's diaper.
In 10th grade I cleared a whole locker room. JV, about 25 players. Locker room is not really lockers, but cement benches with wood frame and wire mesh cubby holes to store our shit, and change in to uniforms. I let a SBD and acted like nothing happened. Slowly it spread, and all the JV football team exits moaning and pissing about the smell, and is standing in the hall where the showers are, then they look back to see me still sitting there laughing my ass off at my locker.
THE...BEST....EVAH though, I was in a Movie Gallery. Just walked in, and there was a long line at the checkout with this hideous looking fat lady at the end. Everybody in line is facing away, others in the store are occupied looking at movie selections, as I make my way right behind her and just as I'm getting there, the urge hits me, and in a very quick thinking fashion, and with lots of luck that NOBODY saw me, I ripped a MAJOR ass flapper just as I pass behind her, and almost simultaneously, I recoil, look over my shoulder at her and scream "dear God lady!" It was loud enough to be heard throughout the whole store. I move on about my business like all is cool, and she's left with the icy stares and kids pointing and laughing at her. My girlfriend was with me, and was savvy enough to play right along. Wasn't planned, just by the grace of God it worked out, and was funny as shit. My GF about shit her pants trying to contain her laughter in the store, and was laughing so hard she was crying when we got in the car.
That happened, and can't be topped by anything real IMHO, but feel free to tell one you think is better.