Pricks on the inside.... as that tired joke goes. I'd have behaved just as you did, from what I gathered from your post..... semi-cautiously, with a defensive mindset, and a spirited attitude. You're in the new "fast 3", and it will be a magnet for anyone with a modded anything-bimmer. I've not experienced the concentration of ego that these events must attract, but the number e36/46 M3's and ambitious or modded sub-M's that solicit a race on my daily commute home is astounding. It's almost always bimmers that even notice my car, save for the occasional ZVQ or american muscle. Ignore, and drive as you would normally is my only advice. Must be hard under such circumstances, but this situation is a hair from death if you start playing with a 18yr old in a S/C 328 who's certain that he has his own modded version physics in play.
BTW, the most offenive BMW owner EVAR is ///M_owns_you, and he's "banned" and sitting on crumpled iForged blocks for the time being, so that rules one turd out of the line up of likely perps.