Oops, it doesn't look like 'wear your grey jogging bottoms to work day' is a national day..

Other days

Eat What You Want Day

Chocolate Milkshake Day

Hannah Day

Gallery Day

Stress Awareness Day

African Immigrant And Refugee Hiv And Hep Awareness Day

Appreciate Yaself A Lil Extra Day

Polyamory Day

One Day

Bow Tie Day