Doppelganger

While walking through the treatment room at the clinic recently, one of the patients caught my eye and smiled.  He was an elderly chap who I knew I had talked to previously but couldn't remember a single thing about.  So I went over and 'fessed up:

PTR

Hello.  I know I've talked to you before but I can't recall what it was about.

Gent

It was this cut on my arm.

PTR

Really?  And it's still a problem?

Gent

Well I only did it two days ago.

PTR

Oh, but I haven't seen you for a least a month.

Gent

[Crestfallen] Oh.  I thought it was you that I saw.  It was a young doctor.  Tall and skinny.

PTR

Ah, that was probably Dr MacGillicuddy.  He must look a bit like me because a few people have mixed us up.

Gent

Yes, tall bloke.  Big nose.

PTR

I see.