I was cycling up Eversholt St., (London) which is a straight road with very few junctions & a lovely new road surface, so you can get up quite a bit of speed. As I was battling into a headwind, a van started to pull out from the right. I started to slow down in case he actually pulled out on me and then I felt a huge bang on my back wheel. It turns out numpty cyclists had decided to slipstream my up Eversholt St. and seemed to think it was a bit funny that he hadn't been able to stop when I slowed down. I explained to him why slipstreaming someone who is unaware that there's someone on their back wheel, and esp. in an urban environment, isn't very sensible. Whether that go through to him is a different matter. Bloody numtpy. Grrr...