I don't really know anyone that was ecstatic that UConn lost. It was more like a "meh" moment for me.
I even have a friend that was a Women's Basketball Manager at Tennessee and he wasn't even as excited about them losing as you are.
Do we hate winners? I don't know. I don't like the Yankees, mostly because they are in the same division as the Orioles, but I have no problem with the Lakers or Patriots. I guess I enjoy watching greatness and to be able to say I saw a team win 90 games in a row or I saw a team finish the regular season undefeated or I saw the greatest player to play since MJ (I'm talking about Kobe).
I get frustrated when the Yankees or Duke win, but it doesn't ruin my day and it certainly isn't "the best day of my life" when they lose.