Fic rec: "Hello, Half-Blood Prince"

Harry/Severus (well, sort of) fic, after HBP? Light-hearted, humourous HP/SS fic, after HBP? It's hard to imagine, but Acid has done it perfectly. If you haven't already, run over and read "Hello, Half-Blood Prince" -- because after that book, we all need a little Snape humour. :D

Note: do I really have to tell you there are spoilers?