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

Other days

tulip

Tulip Day
cursing

Cursing Day
lisp

Lisp Day
pick me

Pick Me Day
ormille

Ormille Day
my little pony

My Little Pony Day
kiss a brunette

Kiss A Brunette Day
cat girl

Cat Girl Day
boba

Boba Day
reading

Reading Day