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

Other days

bubble bath

Bubble Bath Day
ruby

Ruby Day
donate your hair

Donate Your Hair Day
brow

Brow Day
ask out your crush

Ask Out Your Crush Day
tell a fairytale

Tell A Fairytale Day
one

One Day
promposal

Promposal Day
gum

Gum Day
slime

Slime Day