gabby-mouth
A 'gabby-mouth' is someone who yells, talks nonsense, and won't stop talking even when you beg them to be quiet.
My friend is a gabby-mouth. She talks about her crush every time we hang out.
My neighbor is a gabby-mouth. He yells about his lawn at 3 a. m.
My teacher said my class is a bunch of gabby-mouths. We talk too much during tests.