I dunno about esp but I've known....2 or 3 sets and it drives me nuts when I'm out with them. They complete each other's sentences etc. I worked with 2 (in different departments thank god) and even though they didn't live together, they'd show up to work wearing the same clothes. You'd see one in the hall and say "Hey Kevin" ummm I'm Keith lol....FUCK it drove me nuts.
And for the record, they DID admit that they swapped out girlfriends when they were younger. The stories they had......