Ah yes, the super-competitive commuter who doesn't get drafting. That happens to me all the time, Sprocker.
I ride in from Wimbledon train station to Hammersmith each day on Brompton; you quickly get to know who you can take turns with, and who is mortally offended by someone who is quicker / able to pace them on a clown bike.
There's one guy in particular in day glo who runs every single red light if he knows I'm behind him (I assume it's the same if I'm up ahead) and starts pulling all kinds of daft stuff to shake me off. Of course, if I offer him my wheel, he feels obliged to get past me, rather than sitting in. At that point I always engage Sturmey Archer 3 Speed Power (tm) and shake him down. But I don't sit on his wheel if I can help it, because he just becomes an incredibly dangerous rider. In the past, I've sat back so as not to put him and other car drivers and cyclists in danger. Mind you, he rides semi-douche anyway - I just try and avoid pressurising him into full douchebag rider mode...
That said, there are a bunch of regulars who are all good for a bit of drafting and turn-taking, so bumping into them - even if we don't exchange more than a couple of words - always makes my commute a lot better.