Of the many happy campers at the record-demolishing (and economy-confounding) Sotheby’s auction last night, Takashi Murakami may have been the happiest. Drawing stares from art-world veterans — one told us she’d never seen an artist show up to watch his own work on the block — the Japanese Pop maestro sat in the back of the room with a serene smile as My Lonesome Cowboy, his larger-than-life sculpture of a boy waving an ejaculate lasso, brought in $15.2 million —