I find it both crazy but intriguing that this was Doctor Jerk's first ever fandom.
Well....TECHNICALLY the first place I found stuff was the Phineas and Ferb Fanon Wiki(although at the time I didn't know what fanon meant) although those were CONCEPTS and not actual fics.
The first TRUE fanfic I read...........it was either "Snoopy vs Kat" or the Atomic Betty Kid Vs Kat crossover.
Although after reading all the Kid Vs Kat Crossover fics(I remember the Courage one being ok) I moved to reading Spongebob crossover fics and stayed there for quite a while(for a time I didn't know about NON crossover fics)