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

Other days

boyfriend

Boyfriend Day
boy friend

Boy Friend Day
get funky

Get Funky Day
lisp

Lisp Day
kale

Kale Day
book

Book Day
my little pony

My Little Pony Day
nail polish

Nail Polish Day
bow tie

Bow Tie Day
nae nae

Nae Nae Day