I consider myself to be a competitive commuter. I think I invented the term, but certainly not the concept.
Part of the competition means that I don't like getting passed. In fact, I tend to target the next rider I see and pass them (honestly, its just a goal and doesn't always factor into reality).
Nevertheless, when I passed a woman a couple of days ago I knew I was in for a fight. She was clearly out for a "riding to lose weight" kind-of ride. She was on a very busy (read: dangerous) road, wearing flip flops, no helmet, red as a beet and I could hear her breathing from 20 feet away. I gave her a friendly wave...
In spite of it all, she had venom in her eyes when I passed.
About a mile later I was stopped behind 2 cars at a red. As the light just began to turn she whizzed by me, missing me by about a foot.
I had already seen her go through one red light so I was in no mood to play her game. Instead I slipped into her wake and leisurely drafted her for about two miles before she turned.
I think the drafting really annoyed her all the more. I don't believe she knew what I was doing and was confused. Maybe I was playing the game after all.
Update: I passed her going in the other direction again this morning. It was at a red light and she was on the other side of the intersection. We clearly saw each other seeing each other, and I'm sure there was recognition. Then she turned, pedalled and went through the red (!).