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

Other days

frozen yogurt

Frozen Yogurt Day
singles

Singles Day
aloxolt

Aloxolt Day
carpenters

Carpenters Day
get funky

Get Funky Day
stress awareness

Stress Awareness Day
youth

Youth Day
bow tie

Bow Tie Day
ruby

Ruby Day
martini

Martini Day