Oops, it doesn't look like 'be an arsehole day' is a national day..

Other days

stud

Stud Day
hiv awareness

Hiv Awareness Day
blanket fort

Blanket Fort Day
cursing

Cursing Day
offer

Offer Day
brow

Brow Day
ruby

Ruby Day
kale

Kale Day
boba

Boba Day
boyfriend

Boyfriend Day