INSET day 

A day off school in England which is mainly used for sleeping and eating or seeing friends
Its used for teacher training

Girl 1: OMG its an INSET day on friday!! lets go shopping!!
Girl 2: OMG yes!!!!

INSET day by dr-who-rocks June 21, 2012

Meese Day 

July 1st Holiday Celebration in the Loadout video game community.

This comes from the Loadout Community where a non-native english speaking player was attempting to ask about Canadian holidays and if, in fact, Canada had a day celebrating the "meese species" in chat. After some confusion it was discovered that he was asking if Canada had a day celebrating the moose. It snowballed from there and has taken over the entire community.

Meese Day was first celebrated July 1st 2013.

I'ts July 1st. Happy Meese Day!

Meese Day by Duran Vega July 25, 2013

J Day 

A holiday celebration paying tribute to His Airness on the 23rd of each month, plus an extra J Day on February 3rd (2/3). Commemorators honor his glory by wearing Air Jordan sneakers/apparel, listening to rap music making reference to Michael Jordan, watching/quoting Space Jam, smoking J's when appropriate, and other assorted MJ related activities.

"Picked up some fresh 11's for J Day next month"
"J Day, nigga. J Day!"

J Day by thebonedaddy March 28, 2015

good day 

the same as Fuck you but for 1890's

John how is your wife Dave

Dave Good day
(Dave pulls out musket and shoots John right then and there)

good day by asdfghjkl1qqwertyuiop2zxcvbnm3 October 27, 2019

Groundhog Day Disorder

A lightweight sounding but serious mental illness that consumes some people to the point of living for that single day of the year when Punxsutawney Phil emerges from his hidden place; what’s worse is the full picture of obsessive preparation often leading to ruinous financial consequences and severe social isolation that sometimes accompanies this devastating disorder.

Somehow I never suspected that my brother was suffering from Groundhog Day Disorder, but when we found out, it all came together and answered so many previously unanswered questions.

Groundhog Day Disorder by Dr Bunnygirl November 18, 2019

Gamerco98 Day 

December 12th is Gamerco98 Day. If gamerco98 is in your discord server he must get owner for this one day to do whatever he wants.

Oh shit its Gamerco98 day. Better give him owner or else I'll end up in hell.

Gamerco98 Day by Jesus Christ v20000 December 11, 2020

Pablo Day 

The Day we Come to Celebrate a Man Named Pablo on March 11.

It's Pablo Day My Dudes, AAAAAAAAAAAAAAAAAAAHHHHH.

Pablo Day by Detective Dumbass March 11, 2021