I work in an office of four. Literally four. And they're planning to order pizza for a "Christmas Party" here today. I'm not wanting to partake in the pizza, especially since I've got perfectly good leftovers at home I need and want to eat. And besides - the only pizza available in my town isn't worth the wasted calories.
So they just asked me for the first time if I wanted pizza - they just assumed I wanted some before now. I told them no, I'd be going home to eat.
And now they're upset....I'm trashing the holiday atmosphere. So I'm about to head home for lunch and then sit in my office while they're all in the back eating pizza and cookies and having a good time, since they'll give me a hard time for not participating. They always do.
In a bigger office it wouldn't be so hard or awkward. But when 1/4 of the office isn't participating, it's weird. Blah.

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Let us know how it went...