Poseidon was angry at Odysseus for three reasons. First, Poseidon supported the Trojans in the Trojan war and Odysseus was a member of the Greek forces that defeated the Trojans. Second, the goddess Athena was the main patron of Odysseus and she was a rival to Poseidon, having beaten him in the contest to be the patron deity of Athens. Third, and most important, the Cyclops Polyphemus was the son of Poseidon. In book 9 of the Odyssey, Odysseus and his men blind Polyphemus. Because Poseidon is god of the sea, offending him caused numerous delays in Odysseus’ sea voyage home.
Odysseus angered Poseidon, the god of the sea, when he blinded Polyphemus, the Cyclops, who is Poseidon's son. Odysseus and his men escape from Polyphemus' island after cleverly hiding themselves under the Cyclops' sheep to leave his cave. While inside the cave, Odysseus told the Cyclops that his name was "Nobody," but as they're leaving the island, Odysseus cannot resist the temptation to brag. He yells his real name so that Polyphemus will know who managed to trick him. In response, the Cyclops prays to Poseidon and asks him to destroy Odysseus' ship. If Poseidon won't do that, Polyphemus then requests that the sea god delay Odysseus' return home for many years, so that he comes home "a broken man--all shipmates lost, alone in a stranger's ship and find a world of pain at home." Poseidon hears his prayer and makes trouble for Odysseus for many years.
You can find your answer in part of Zeus's speech -
"That Neptune is still furious with Ulysses for having blinded an eye of Polyphemus - the king of the Cyclopes. Polyphemus is son to Neptune by the nymph Thoosa, daughter to the sea-king Phorcys; therefore though he will not kill Ulysses outright, he torments him by preventing him from getting home. Still, let us lay our heads together and see how we can help him to return; Neptune will then be pacified, for if we are all of a mind he can hardly stand out against us.
i hate you all thats why hahahahahaha stupid now what
Poseidon was angry at Odysseus because he blinded his son, Polyphemus and because he supported the trojans in he trojan War