That I would recognize him on sight would mean we are pretty much the same person. I would then ask him, or her if they are from a reversed gender universe, for the security code I had prepared just in case something like that happened. No matter what they answer, I would say that I did not have a security code.
That should take care of anything pretending to be me, as they would know that the insistence of no security code was actually a second level to the question. There IS a security code, and I am not saying it online.
If they could prove they were me, I would go with them. If they have dimension hopping technology, I would kill him (as obviously he's an idiot version of me, as he would have totally done the same thing were he in my shoes) and travel to a universe/dimension I know like the back of my hand, and seize eternal youth. I would then go around gathering power until I launch an attack on the multiverse and become the dark, evil overlord of as many universes as I could.
TVTropes' Evil Overlord List and all documents related to it would be read on a weekly basis.