I like the Celtics too!
I probably cheer for green and gold laundry (NFL, not NBA). Part of that though is that I just have so little time to watch sports these days and what tends to happen is sort of grandfathering -- tune in for Brett Favre, get to know Donald Driver, on through Aaron Rodgers and co. It's much more fun to root for the guys you know (if you like them anyway!)
Brett Favre is who made me a Packers fan, (I was a Vikings fan before that) so that was not very laundry-ish though it was easy since I was in WI at the time. But once that happened, I know the team well and I'm rooting for them. (And they're the Packers! They're plain cool.
I was a rabid Bulls fan when I lived in MN, that wasn't really laundry but it sort of was, this was pre-Timberwolves and so if we were casting around for non-hometown teams, the Bulls were both nearby and fantastically good (although I started to become a fan just before Michael Jordan came on the scene, so I wasn't a Johnny-come-lately).
And I guess that's a big part of it too, the johnny-come-lately/ fair weather fan part. It sucks when times are bad for your team but it's so so much more fun when they finally do well if you've suffered through all the bad parts with them. Feels more earned (which is silly, we're fans, we just watch).
But I know exactly what you mean about the Lakers, I went through the same thing. They were good when I lived there but I just can't stand Kobe. (I like Shaq actually.)