I hate to say this but... Never knew the British flag, the Union Jack was oriented a certain way until I came across the BBC News reporting the mistake made at the UK-China Ceremony earlier this week. Notice the pattern isn't symmetrical and the upper-left white diagonal stripe should be thicker. So in other words, that corner of the flag should be attached to the pole or, be in your right hand when holding it.
I don't think one could make a similar mistake with other flags when they're all clearly asymmetrical at a glance.
Full details can be found on Wikipedia about proper use of the flag and how it came about.