As often happens, you pull up alongside the same bike a number of times if you're both going in the same direction and have to stop at lights, etc.
Anyway, this guy - who would have been in his mid 40s - wouldn't acknowledge that a fellow rider was next to him, despite the fact that we stopped next to each other about 4 times and I would look over to say hello!
The last straw was when he was stopped in the right lane and I was in the left, the lights changed and he proceeded to take off and veer straight into my lane!

What is it with some people?? Bike riders are usually such a friendly lot
