In the lines 1 from 18, Macbeth is very rude with the servant and he didn't believe what the servant says anymore. He also continuously insults the servant when he says, “Go... thy face and over... , / Thou lily-livered boy. What soldiers, patch? /... Those linen cheeks of thine / Are counselors to fear. What soldiers, whey-face” which are in lines 14-17. Also, Macbeth depicts the servant as a coward and a clown. Hope this helps.