Open your mouth and you'll put your foot in it; fools are the ones who love to talk.
Literal
Things say-[if-ば] lips cold. Fools as-much-as want-to-say.
物言えば唇寒し is a famous phrase attributed to Matsuo Basho, meaning 'if you speak, your lips grow cold' — speaking invites trouble. 馬鹿ほど言いたがる means 'the more foolish someone is, the more they want to talk.' Two proverbs combined.