I don't, however. Wouldn't want them walking away, thinking they were right all along and this one is definitely the evil one, now would we?
Maybe they watched Sabrina the Teenage Witch episodes with Sabrina's evil twin (from an alternate universe) Katrina. Maybe they played Legend of Zelda and saw Link's evil twin Dark Link. Maybe they are Trekkies who saw Star Trek Nemesis, and since they watched a movie with Data and his evil twin B-4, they are now twin experts. I could go on and on with examples.
I am not even going to go into soap operas' use of the evil twin. It's just not a good soap if someone's not coming back to life after being offed by their evil twin, right? Katharine Chu wrote a paper, up on MIT's OpenCourseWare, about the decline of the soap opera. She's got a whole paragraph on the evil twin plot twist.
To be fair, a lot of "evil twins" in the media are actually evil, or misunderstood, doppelgangers, not identical twins. But people don't always... oh, alright, NEVER pick up on that subtlety.
Now, if you'll excuse me, I have some