So many gorgeous touches in this! I'd be here all day if I mentioned all my favourites, so I'll just pick a couple at random - Harry's underpants obsession when Regulus is using Legilimency on him, and Snape delaying orgasm by picturing Dumbledore pole dancing *giggles*
Oh OK, one more: Harry's line to Snape's mum when she says she'll be in the Hogs Head.