Oops, it doesn't look like 'handshake event one day' is a national day..

Other days

lost sock memorial

Lost Sock Memorial Day
camera

Camera Day
gum

Gum Day
nail polish

Nail Polish Day
nae nae

Nae Nae Day
prosecco

Prosecco Day
lisp

Lisp Day
hoodie

Hoodie Day
one

One Day
bubble bath

Bubble Bath Day