Normally, coupes are exercises in vanity: all fluff and no substance. Ego-trumping sensibility. Liberace bitch-slapping Alan Greenspan. No one knows this better than BMW, which has been in the 3 Series game since Gerald Ford was cracking his knuckles in the Oval Office. It’s getting pretty good at the game, as evidenced by the outstanding latest version of the 3 Series, which debuted as a 2006 model in “E90″ sedan form only. As in previous generations, the coupe version is released just when the panting over the sedan has subsided.