"Jamais Vu" by Julia Williams

They agreed that birthdays were ridiculous once you got past thirteen. Ditto Christmas. Instead, they developed a system of generalized reciprocity — a two-person Kula Ring, Amelia called it — swapping gifts only on holidays like Shrove Tuesday or St. Patrick’s Day.

Mildred’s sixteenth birthday — four months to the day after Amelia’s — they would observe by sneaking into the worst bar in the city. Which bar this was, they hadn’t decided. Until now.