Bob: He was probably just some random guy pretending to be me.
This is the first time I've seen you in person for a while.
I haven't seen you at all for a few months.
What? We have been talking for a few months online, remember?
No, I was never talking to you online.
The username was B0b12364
Ummm, that's not me.
To prevent this, always have a unique username. Tell your friends that you are going to send them a friend request. Don't accept random requests from people you don't know. If you get a friend request that seems to be your friend make sure that it is the person that you think.