...you've overtaken another cyclist, he's in secondary position or worse and you're in primary. Cars pull out from a side junction in front of you and you have to slow down, so you stay in primary in the traffic. You've slowed down sufficiently that the guy behind has made up the 40-50 yards you were ahead of him, and he slips into a fairly fat secondary position to your left; every time you move forward, he keeps far too close to you, right on your left. He tries for the occasional dart down the left hand side of the cars, and he's clearly tiring because you and the cars ahead are going way faster than he was when you went past him, but his testosterone driven desire not to be 'bested' by another cyclist has taken over. He's in the way and, frankly, embarassing. What do you do? You can't just out-accelerate him, theres too much traffic. Do you put up with him? Do you talk to him? Do you slow down and let him go?