Once a year at the Scranton Business Park, a man comes around with a small oven and some soft pretzels as well as toppings. One complimentary pretzel is given to whoever works in the building and waits in line. It is seen in the episode "Initiation". This idea was created by Billy Merchant, the building manager of Scranton Business Park.
Stanley Hudson is especially fond of this day, mostly because it is a break from "a job for which he gets paid too little." Stanley is also the originator of unofficially naming this day "Pretzel Day".
Erin screamed "Pretzel Day" in the hopes of getting Stanley to wake up and get out of bed in the episode "Tallahassee".
While National Pretzel Day is celebrated on April 26th, the specific date of the annual pretzel day celebrated by Scranton Business Park is not known, but must be between September 1st (the date of the preceding episode) and Diwali (celebrated in late October or early November). A perfect candidate date to commemorate the event would be the original air date of this episode, October 19th.