Flannelmouth

"Oh!—Oh!—Oh!" Bert screamed, with every blow she struck "Hey, old flannel-mouth! Watch out! You'll get yours in a second."

Source: wiktionary

[Y]ou may detect your own "elderly" tricks—pushing your shoulders up around your ears, being a mumble-boy or a flannelmouth!

Source: wiktionary

How do they sit there, hour after hour, and listen to the congressional gasbags without blowing their tops? . . . never once leaping over the table, grabbing an inquisitor by his ears and screaming, "Hey, flannel mouth—does the phrase ‘posturing hypocrite windbag’ ring a bell?"

Source: wiktionary

Uncle Sedgwick, who is considered around and about as somewhat of a flannelmouth, has talked Drizzlepuss into going ice fishing. . . . Uncle can tell you some wonderful fish stories, but, boy, I've never known a guy who's so careless with the truth.

Source: wiktionary