If you aren't paying attention to the name tags, you could well be explaining some C curiosity to Kerninghan, explaining longest common subsequence to someone who wrote the diff for unix. They would listen to you patiently and thank you. May be also subtly point out an error in your argument, while you never realize whom you were talking to, until much later.
The Kerninghan incident did not happen, but several similar incidents did.
Down voter: I assume you disagreed with my opinion and not that there is anything unsavory about the comment.