Are you trying to use your manners and not say the word, 'fart'???
Just kidding!
Well - that's a good question. If they do it purposely, I think it's pretty darn gross. Maybe they just have never been taught by their elders not to do it (or their elders taught them it was an ok thing to do).
Could be a medical condition and they just can't hold it in.
Just don't stand in the line of fire, Dede and you'll be ok!