1to talk drivel
2not to know what one is talking about
3to assert sth without a proper understanding or basis in fact
Examples
bú shì不是xiā shuō瞎说，wǒ我zhè这fèn份gōng zuò工作zhēn shì真是méi jìn没劲！
不是瞎说，我这份工作真是没劲！
Do not talk nonsense, My job is very boring!
瞎说！
Nonsense!