[Miss Marple]

Well, all I know is what I read on several sites before I replied to you, most written by British people. Snopes also has an explanation which is the same as what I posted.

Perhaps your friends were religious and did this as a personal choice, so that they personally could avoid gift-giving on Christmas Day.

MadIvan, what is your understanding of the origin and purpose of Boxing Day?

[expatpat]

See #41. Your powers of detection seem to be slipping -- Jane Marple should know!

[1066AD]

Your explanation of Boxing Day is correct.
It's when you also start on the cold turkey sandwiches and perhaps go beagling !