Azumanga Daioh, I had heard of it by name only before attending Kumoricon 2006, so I saw the chance to see it in a viewing room there and checked it out. I walked in at a very bizarre moment that, without context, left me absolutely baffled. I left the viewing room with my brain oozing out of my ears, swearing I'd never watch the show again.
Not a couple weeks later, I had bought the first volume of said anime, and loved every second of it. To the day, Azumanga Daioh is one of my favorite anime.
Thank you/I blame you, Kumoricon!