I think the first one I ever watched was "Jet". My younger brothers were hooked on the show and would whine and complain for ages if they missed any "Avatar" (for some reason, I thought it was some sci-fi type thing. Don't ask why, lol).
Then one day I was reading a book in the lounge room while they were watching, and so I watched it too. Slowly started to like it.
Funny thing is, now I'm even more obsessed than the two of them combined. Suppose its because I have more access to internet/spoilers/speculation
Avatar FTW! *waves Avatar flag*