This is gross but I think makes perfect sense. I think the reason people (generally) dont mind the smell of their own farts as much as other peoples' is because their smells are associated with relief at that moment. Smells are powerful- perfume while you're at a concert or some food smell while you're talking to someone- that smell turns you on or off to that moment and associates with that moment. If you smell something bad or good during a neutral moment, it can color your interpretation of your enjoyment of the moment, and conversely if you smell anything during a good or bad moment, it can color your interpretation of that smell, associating that memory with that smell for a long time...