it should be 扯淡,and it is a dialecticism。
1.In Chinese dictionary,one of meaning 扯 is talking aimlessly.For instance 胡扯(huche),闲扯(xianche),东拉西扯(donglaxiche)。
2.one of meaning 淡 in dialecticism is something which doesn't make sense.
So the meaning of 扯淡 is to chatter thoughtlessly or indiscreetly,it is a verb.