Tell the stall owner that you “need to find the restroom to barf up eggnog from a few stalls back.”
Lift up your shirt to reveal a series of insect bites. Tell the stall owner that they are messages from Insect Santa, who needs your help immediately.
Tell the stall owner you just sustained a Christmas-tree-related injury and need immediate medical attention.
Tell him you just sustained a menorah-related injury and need immediate medical attention.
Tell him there is snow in your eye and you need immediate medical attention.
Explain that the last time you brought baubles into your home, you woke up in the middle of the night, at the foot of your Christmas tree, chomping on bauble shards. Tell him you’d rather not pay those medical bills again.
Tell the stall owner that you’ve decided you don’t love anyone anymore, and so won’t be buying gifts this year.
Tell him that you’ve also decided you don’t love yourself anymore, and so won’t be getting anything for yourself, either.
Let the stall owner know that you feel “magic in the air,” but then act as if you’re slowly realizing that what you thought was “magic” is actually a horrible fart.
Tell the store owner that you had a bad experience with wreaths as a child. He will likely not ask for more details, but if he does, tell him that your parents joined a cult in which they played horseshoes with wreaths instead of horseshoes. Nothing else major happened in the cult (mostly just wreaths used for lots of things, such as necklaces and Frisbees) and soon enough it was disbanded. But then one day your high-school friends suggested a game of horseshoes, and you said, “But we don’t have any wreaths,” which led to a very embarrassing conversation.
Tell him you’re an elf in disguise, so you basically have everything you need, holiday-wise. You’re just there surveying the competition.