A case of mistaken interest

Just a quickie... there's a guy here in the office who for some reason thinks I'm into Moto GP (the motorbike version of F1 Grand Prix). When I started in this office a few weeks ago, I mentioned, and got talking to, this guy about motorbikes, and the fact I used to ride them etc. And now, for some reason, he thinks I am a massive fan of the Moto GP stuff, and whenever there's been a race at the weekend he comes in and says things like "did you see the race?" and "such-and-such (some racers name I don't know) threw away his title chances" etc. etc. How can I tell the poor misguided fool that I have no interest in the sport?! I just have to smile and say things like "really? Cor!" and "No, I don't believe it!" and stuff... daft eh?