I'd say he just spotted me with all my lycra and stuff and thought he'd teach a cyclist a lesson as he was an inadequate wonker who just hated mamils.
Or, y'know, he slowed down on the approad to a junction to see what was coming and then misjudged your approach speed, in the way that a lot of drivers do when they assume that cyclists are always extrememly sllooooooowwwww. That's if, as I think you are saying, you were cyling along a road and the driver in question was joining that road from a junction with a 'give way' on your left? In that case, you should be able to expect them to give way but they might have made a different decision if they misinterpreted what your speed/road position/intentions were. Still rubbish driving, poor observation, bad decision making and all that - but not necessarily malicious.