Gym farts aren't funny. Ruins my consentration. I'm so glad that I carry around my Fabrege air freshener when I work out at the gym. When some big galoot toots at me, I spritz him back. My favorite scent for the gym is "poppy seed."
They are hysterical in certain circumstances. Its bad when you are in the middle of your run and some man or woman within a one meter radius lets loose the dog of war and you're stuck sucking in shit air till it dissipates...
I've farted only about twice at the gym and they were both while doing jump rope. Its hard to squeeze and jump at the same time. Luckly it was covered up by the smack of the rope on the floor.
Like I said, one mostly hears people butt trumpeting in Ab classes. These heavy set people get in there and strain so hard to lift they doughy bodies they can't help it...