The Golden word of English Literature!
It is mimed behind people's backs to suggest that they talk too much or that they talk about useless topics for no reason.
It is also viewed as a word expressing indifference, or lack of a preference.
blah is sometimes assumed to mean something negative because it is used to replace a word that may be unpleasant, but blah itself is neutral.
"Blah! Blah! Blah!"
"I Feel Blah!"
"Blah! stop your crap!"
Being whipped by Pebbles/Sandrock