耍贫嘴 is a colloquial verb meaning 'to talk glibly, to chatter endlessly, or to crack silly jokes'. It carries a mildly negative or teasing tone — you use it when someone talks too much, says things that aren't serious, or tries to be clever with words. The structure is a separable verb (离合词): 耍 can split from 贫嘴 when adding duration or objects, e.g. 耍了半天贫嘴 ('chattered for ages'). It's informal and common in everyday conversation, especially in northern Chinese dialects.