Someone shouts "Oi! John!" to your end of the pub. You and six other people, all called John turn around. It's a case of mistaken identity. The person was calling at another John.
A vow is made. This won't happen again. From now on, you will answer to "Kate" - after all, there are a lot less Kate's in the world than John's, and it's hard to mistake a 15 stone bleached blond bearded beast (don't you practise your alliteration on me) for the usual Kate.