Politeness requires that one should try not to make a noise when expelling anal gas. It similarly requires that one should not make a noise upon discovering expelled anal gases. Thus society continues in a mutual agreement to ignore the occurence.
My father used to say "you're like a fart in a colander" to indicate uselessness. I don't know why that has just popped into my head or even why I'm bothering telling you lot, but there it is.
I think it's about time we invented some sort of pants-catalytic-converter. We take pains to minimise every other bad smell our bodies produce, so it would be quite in keeping.
(st d) I think burping noisily is more offensive (in a polite setting) than farting. You can always do it silently and the "product" is inoffensive. No-one need know. But you can't get away with a fart, however discreetly expelled. (Projoy) Now, there's a challenge I can't ignore, as a chemist. The simplest answer would be an appropriately-shaped pellet of activated charcoal taped to the bum in a gastight manner. It would need to be kept dry and be easily removable for obvious reasons. It would eventually (a month or so) become "full", so to speak, but could easily be regenerated by heating in an oven, the only problem being that everything it had absorbed would be driven off. Extractor on full blast, I feel. snorgle has got in while I was writing this and the link says it's been done already. I bet it's activated charcoal, though. Just a question of how you fix it.