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

Other days

aloxolt

Aloxolt Day
lisp

Lisp Day
gum

Gum Day
singles

Singles Day
first love

First Love Day
boy friend

Boy Friend Day
kale

Kale Day
tulip

Tulip Day
martini

Martini Day
bow tie

Bow Tie Day