Odysseus essentially calls Polyphemus stupid, gullible, and easy to outsmart. He does this as he is going away from Polyphemus' island. Up until this point, Odysseus effectively kept his identity a secret, but pride welled-up inside of Odysseus for a few moments and he felt the need to let Polyphemus know who he was so that Polyphemus could tell everyone who the great man was that had conquered him. Unfortunately, Polyphemus used that information to pray to his father Posideon to hurt Odysseus. Thus, Polyphemus could call Odysseus stupid too.
Odysseus tried to call Polyphemus a poor host for not sharing his wealth with poor traveling guests. Polyphemus could call Odysseus the most terrible of guests because not only did Odysseus bring a gift, he used it to manipulate Polyphemus by getting him drunk, but he also stole Polyphemus' sheep!