to never stop talking; to talk too much [colloquial]
Definitions (粵典–words.hk)
形容詞
好識講嘢，甚至唔係好識做其他嘢，只係識靠把口 to talk too much; One only knows how to talk but not to do other stuff; literally: all the body parts are dead, except for the mouth
講嘢好叻又有咩用啫，咪又係死剩把口？
讲嘢好叻又有咩用啫，咪又系死剩把口？
What is the use of knowing how to talk? It's just bullshitting with no use.