口不擇言

to speak incoherently / to ramble / to talk irresponsibly

mouth / classifier for things with mouths (people, domestic animals, cannons, wells etc) / classifier for bites or mouthfuls

no; not so / (bound form) not; un-

to select / to choose / to pick over / to pick out / to differentiate / to eliminate / also pr. [zhai2]

words / speech / to say / to talk