My birthday is on the 22nd of December. This year I will have suffered 31 of the blasted seasonal things.
Its rubbish because:
This year it's on a Friday. People will, as they usually are, be finishing ogg their last minute Christmas bits/going on Christmas do's etc and so won't be available for a get together.
Even if they were, the places will be packed as it will be "Mad Friday"
Because I want to buy all sorts of stuff, as I do every year, but can't incase they get bought for me for Christmas/Birthday. This time of year I usually end up wanting to buy duvet sets. pjs etc for myself but have to hold off til after Christmas to get hem incase someone has got me some for Christmas.
As they're so close together, I never know what to say when people ask for gift ideas.
....Add in your suggestions to counter to above, or reasons why your December birthday is rubbish.