Don't get me wrong... I do know when people are there. In this case I knew someone was behind me, I signalled a stop at a stop sign, and the guy behind me decided to run the stop through me. If someone wants to come up to me and be social while I'm riding that's fine, I will reciprocate (and have done so). But coming up on my wheel and sitting there is not being social. And sitting on a stranger's wheel, you have no expectation that they know you are there, will signal, etc. I prefer not to deal with it so I will usually just ride away.