Not quite the same, but some years ago, I worked with a little team of 10, (6 women and 4 men,) and we got on well, and had 3 (sometimes 4) meals a year out, and the Christmas meal was our favourite!
For our Christmas meal, we would finish work at 1pm on the last day of work, and the meal would be at 2pm, and we would get full and fat and merry, and share taxis home at about half four. Our other meals would be in the evenings...
This went on for 4 or 5 years, and then out of the blue, the area manager - Dave - who was situated at an office 40 miles away, (and lived 50 miles away,) decided to invite himself along to the Christmas meal. He also invited himself to the meal we all had together in mid May (that we had because 4 of us had birthdays between 20th, and 25th May.) He had been with the company for 10 years, and worked and lived 40-50 miles away, and suddenly decided to invite himself to OUR meals. 
He was so loud and obnoxious, and no-one else could get a word in edgeways. He just talked about himself mostly, but also kept commenting on how much food the 6 females ate. He kept saying 'where the hell are you going to put all THAT?' And 'that's a lot of nosh for a laydeeee.'
And he would talk VERY loudly, make stupid, (extremely unfunny) jokes, and would look round everyone at the table to see if they were laughing. AND he kept commenting on what all 6 of us women were drinking. 'ANOTHER drink. Not very ladylike drinking so much eh eh eh???' 
I think the 6 of us laydeeeeeez suffered 3 or 4 meals out with him, then just started to make excuses to not go, and arranged our own little laydeee meal for just the 6 of us!
So yeah it is very annoying when someone invites themselves along (or if someone in the team invites an ex colleague, coz they get on with them, when others do not.) Ex colleagues should not be going to a works Christmas dinner IMO.
As I (and some others,) have said, just don't go.