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

Other days

fiancee

Fiancee Day
boba

Boba Day
hiv awareness

Hiv Awareness Day
stud

Stud Day
pumpkin

Pumpkin Day
self care

Self Care Day
latina equal pay

Latina Equal Pay Day
gum

Gum Day
singles

Singles Day
law

Law Day