Hahaha, I laughed when I saw this thread. Can't be to harmful. Unless you have the most methane potent gas ever!
"A" fart, not likely. However, depending on what Stinky McGee has been eating they could be expelling a lot of Hydrogen Sulfide which is the stuff that makes farts stink. Hydrogen Sulfide is toxic and prolonged exposure to it, say on a road trip with stinky McGee, could have minor adverse health effects.
there is no side effects when you smell your fart. but i know you dont like to smell your fart cause you know what will happen if you do