扯淡 is a colloquial, often vulgar verb meaning 'to talk nonsense' or 'to bullshit'. It is a separable verb (离合词): the object 淡 can be separated from 扯 by a measure word or pronoun, as in 扯什么淡 ('what nonsense are you talking?'). The tone is strongly dismissive — you use it to reject what someone says as worthless or absurd. It's common in casual speech but inappropriate in formal or polite contexts.