From Dan Rafael of ESPN today:
Few fans are as passionate as the Brits are when they get behind a fighter like they have Hatton. But as great as it was to see all those thousands who traveled to see Hatton-Castillo (and to hear their inventive songs about him), many of those same fans displayed disgusting and disrespectful behavior. You didn't see it on HBO's broadcast because it happened just before the telecast began, but they booed throughout the American and Mexican national anthems. That's like school on Saturday: No class.
I'm not overly-patriotic, so normally stuff like this doesn't bother me... but it still shows a lack of class.