I read this when it was originally posted and forgot to review, but thinking about it made me grin several times sense. It takes more for comedic fic to impress me than other genres (simply because I happen to think comedy is harder to do well), but this just illustrates how a great writer can make even the most cracked-out concept work.
Both of them were so in-character. Snape was as caustic and bitter as ever, and Harry…well, who else would be so stubborn and persistent to go through that complicated journey and transformations to achieve his goal. Extra bonus points for Patronus-on-Patronus sexcapades.