Tetradactoid

That moment you see a doppelganger, not your own, and begin talking to them like he/she is the person you believe they are, and find out they're not who you thought they were, and emberass yourself by giving too many details about yourself to a complete stranger.

Bro! i got caught in a tetradactoid when i thought i was telling Marcy all about my aching butt from the strap-on she used last night.