It is Fur-Day but it happens on every day of the year.
Niko: Hey Bacon, it's fur-day 4
Bacon: oh no
It's Fur-Day 4 but you have to speak "furry" e.g. "English" is pronounced/written as "Engwish"
Furry: It's fuw-day fiwve (fur-day 5) today!
Person: Ohw now