Lady Psychic
The wierdest slash pairing in the HP fandom that I've read would have to be Teddy Lupin/Cedric Diggory. Obviously, that fic involved time travel (it was a really good story, too).

I've also read a few Severus Snape/Albus Severus Potter fics (I actually like this pairing despite the large age gap). Some other somewhat odd pairings that I occasionally read include Lucius/Harry, Draco/Albus Severus, and Harry/Scorpius.

Also, there was this one fic that I read in which Harry fell in love with two Severus Snapes (a younger one from the past and an older present-day Snape).


I...would read all of those. XD