Also, is it always alright to display the flag everywhere at all times? One of the things I used to hate when I lived in Glasgow was the aftermath of an Orange march because there would be drunken people with a Union flag tied round their shoulders swigging from bottles and if you caught their eye, slurring "You lookin' at me, ya [sectarian insult]?" If I was walking along a street and saw anyone with a Union flag on them in any way in the aftermath of a march - around their shoulders, as a t-shirt, in their hand, swathing their arse, whatever - I would turn around and go the other way.
That doesn't mean the UK flag is evil or everyone with respect for it is evil, of course. That would be totally weird, but it's fair to say it doesn't give all people automatic positive feelings at the sight. I think some groups have hijacked flags and this is why other people find it unnerving.