I don't understand people who support multiple teams, it goes against the whole nature of supporting.
Supporting is something you do because you identify with one team and that's your team for life, pa**ed down through generations. It's unconditional love, through good times and bad times, and comes with an irrational hatred of certain other teams. Every other team is a potential threat to your team - you can't be supporting them!
There's no pleasure in supporting multiple teams because you can't really lose, and that's exactly the problem. You can't really win if you don't have 100% investment in any one thing.
I admire Barca, AC Milan and Man U, but I would never support any of them because ultimately I don't care what happens to them. If they win or lose, it means nothing to me.
That's just me though.
Co-sign
My family back home are die hard AJAX fans, all of them! they despise and make jokes about Feyenoord aaaaaall day long, they don't like PSV either, but they really don't like Feyenoord, lol, you'll find that with most people from Amsterdam.
Due to this I too love AJAX, seeing that AJAX are the only club I have seen play, besides a couple of 1.FC Köln matches, while in Germany (in Cologne it gets a little more interesting by the way, the city has two clubs Fortuna Köln being the other) so the people are automatically divided between the two teams (most suport 1.FC though). Back in the 60's and 70's, 1.FC arch-rival was Bayern München, and they dislike them the most to this day. Even though 1.FC struggles to maintain a spot in the 1. Bundesliga.
I'm surprised that half way around the world, people are as fanatic about their favorite clubs, as they are in the clubs hometown, and that the exact same quarrels play out as they would back home.