Going through the Christmas cards Christmas night, after everyone leaves...
Making a list and checking it twice.
People really do that you know. If they sent you a card and you didn't reciprocate - you are so off their Christmas card list for next year. I actually sent cards to the people I missed last year - the people who dropped me this year because I never sent a card last year. I kind of did it just to confuse them. ;)
FYI - that is so not what Christmas is all about, is it... you know - tit for tat stuff.