What is another word for shooting off mouth?
Pronunciation: [ʃˈuːtɪŋ ˈɒf mˈa͡ʊθ] (IPA) 
The expression "shooting off mouth" can be easily replaced with several synonyms that convey the same meaning. For instance, "blabbering," "yapping," "flapping one's gums," "ranting," and "jabbering" are some synonyms one could use. Other possible options include "spouting off," "mouthing off," "rambling on," and "talking nonsense." All these phrases refer to someone who talks too much without thinking about the consequences of their words. It suggests that the person in question may say whatever comes to mind without considering the impact it may have on others, and hence causing frustration or annoyance.
