The modern interpretation of 'Boxing Day' is a polite term for how some people act when out looking for a deal on the 26th of December. It's a bit like what I hear "Black Friday" is like in the US, although being Canadians it's more of a lot of "Oh, sorry for stepping on your foot / no, you take the last one" than any sort of violence.
It's also the one of the best days of the year to go to Costco -- everyone else is shopping elsewhere and the place was deserted!