Today I answered a question and after submitting I noticed that Jon Skeet also answered. This was the first time he & I had answered the same question. His was the correct answer, so it doesn't apply this time, but how about a badge for a case where someone answers the same question as someone in the top X (10, 100 etc) and gets the answer over them.
Badges are supposed to encourage good behavior. I see none of that coming from a badge like this.