My Mac had made a duplicate ‘me card’ containing just my name and one email address. I found this in Mac Address Book tips: 5 more handy hints on Reality Distortion:

Choosing your own card

When you first set up your Mac, Address Book creates a “me” card with your own contact details. However you might find that you end up with a second card which better represents you – this can happen if, for example, you import your contacts from another app or device into Address Book.

To make this second card the “me” card instead, select it and choose Card > Make This My Card. (You can also locate the “me” card with Card > Go to My Card.)

It’s simple.