Do you know what a “doppelgänger” is? This German word describes your double—a person who looks just like you. (The word translates to “double-goer.”)
Oh, and you also need to know that a British slang term for fart is "guffle." So anyway, over at the British site [b3ta], I just read a funny story by "mictoboy":
You know that thing where you can stand the smell of your own guffs, but not other people's? So you can drop the most rancid fart in the world and sit there quite happily while everyone else is retching
Once at work, I popped into the bathroom and was greeted by the smell of previous occupant's sit-down visit. What utterly freaked me out was that although the farty smell was clearly not my own, I could quite happily stand to smell it. It smelled like I'd done it. I'd unwittingly stumbled on my very own “guffleganger”! I am to this day a little disturbed by the incident.