The holiday was founded on November 15th 2011 when Mr. Fireman had passed out from excessive candy consumption that year on Halloween. After coming to, his cousin, Mr. Ambulance, forces him to weigh himself on the bathroom scale. The scale, as well as kept statistics from Mr. Ambulance himself, reveal that Mr. Fireman has gradually gained more and more weight every year after Halloween. Mr. Fireman eventually comes to the realization that he can no longer celebrate Halloween, otherwise, it may lead to his eventually immobility or even death.
The next morning, Mr. Ambulance wakes up to find Mr. Fireman being interviewed in their living-room during a taping of The Morning Show! With Mr. Davis. Mr. Fireman reveals that he has created a brand-new holiday, called "National Mr. Fireman Day", where he would spend the day doing the things that he enjoyed the most, one of which was excessive candy consumption. Once the taping ended, Mr. Ambulance verbally criticized Mr. Fireman for his idea of eating excessive amounts of candy on National Mr. Fireman Day, as his alternate holiday was designed to avoid that very thing from Halloween and would defeat the entire purpose of the holiday. Nonetheless, Mr. Fireman went on to promote his holiday and many, out of sorrow, joined in on the celebration. By the time October 31st 2012 had hit, millions across the nation had gathered to support "National Mr. Fireman Day".
The holiday will be updated for the also updated series The Lenny Leggo Show The holiday will now be known as "National Jonah Flenderson Day", as Mr. Fireman's character was renamed to National Jonah Flenderson Day for The Lenny Leggo Show.