Oops, it doesn't look like 'side mans day' is a national day..

Other days

boba

Boba Day
bow tie

Bow Tie Day
lisp

Lisp Day
carpenters

Carpenters Day
blanket fort

Blanket Fort Day
cuddle up

Cuddle Up Day
self care

Self Care Day
singles

Singles Day
artists

Artists Day
special education

Special Education Day