The story of Polyphemus and Odysseus gives us an answer to the question: "Why was Poseidon angry with Odysseus?"
As you know, Odysseus arrived on the Cyclopes islands and decided to explore one of them. He took 12 of his bravest men and went to see what was inside a cave that he had spotted from the sea (it was Polyphemus' cave). They found cheese and lambs and kids inside, they ate some cheese and then waited for the master, in order to ask for some gifts from him (i.e. food for the rest of the crew) - at that time, it was usual for a host to give gifts to his guests, it was a duty decided by the gods - the only problem was that the Cyclopes didn't have any respect for the gods and didn't follow their rules.
When Polyphemus came back home with his herd, he pulled a big boulder on the opening of the cave. Odysseus asked him for hospitality, because his ship had been "shattered by Poseidon", but the only answer of the Cyclops was to eat two of his men (I suppose that Polyphemus thought that this person must have made Poseidon very angry, if the god had shattered his ship, so I guess his way to be on his father's side was to eat Odysseus' men).
The next day, Polyphemus and Odysseus had another close encounter, as the Cyclops ate two other men for breakfast. After that, he went out with his herd and closed the cave with the boulder. Odysseus found a big olive stake, which he and his men carved so as to have a sharp point, then hid it under a pile of dung.
When Polyphemus and Odysseus met again, in the evening, the Cyclops ate two more people. Odysseus offered him some wine which he had brought with him from the ship. The Cyclops drank it, liked it and asked Odysseus what his name was, because he wanted to give him a gift, in exchange for the tasty wine. Odysseus answered that his name is Noman (in fact, he told the Cyclops that his name is "Outis", which is a diminutive from Odysseus, but it is a word which also means "nobody". So he was quite sincere, but the drunk Cyclops thought it meant "noman"). But the gift that the ogre had in mind for the hero was not a pleasant one at all: his intention was to "prolong" Odysseus' life by eating him the last.
When Polyphemus fell asleep, the hero, helped by his men, heated the stake in the embers, then drove it through Polyphemus' eye. The giant started to shout and the other Cyclopes came and asked him what happened, had somebody stolen his sheep or wounded him? He answered that "Noman hurt him". When the others heard such an answer, they said that, if nobody hurt him, it meant his suffering was sent from the gods, as a punishment for something he had done - and so they left him to his suffering.
Odysseus was trying to find a way to leave the cave undetected, and his idea was to tie the sheep three by three and hide hid men under their bellies. He himself hid on the fleece on the belly of the biggest ram in the herd.
In the morning, Polyphemus opened the cave to leave the flock out and felt the backs of the animals, in order to catch the sailors, if they wanted to escape by riding the sheep and goats. But he didn't think of checking under the animals, too, so our hero and his men managed to escape to safety.
But the story of Polyphemus and Odysseus could have had a different ending (and we could have had a shorter Odyssey), because the hero, once embarked on his ship, just couldn't keep his mouth shut, even if his men begged him to remain in silence. So he told Polyphemus that he was Odysseus, son of king Laertes of Ithaka (yes, it's true they didn't have Internet back then, so as to know that you don't give away too much info about yourself, both online and offline - but that's no excuse, if you ask me).
The enraged blinded Polyphemus threw a rock into the see, which missed the ship by only a few inches. When he realized he could't hurt Odysseus any more, he asked his father, Poseidon, to punish Odysseus, eithen by preventing him to get home at all, or, if his fate was to get home, at least that should happen after many years, and may all his men perish during the journey, and may he get home in misery (and in the end that's exactly what happened).
As regards Polyphemus and Odysseus' fate, in the end I don't know who ended wors, Polyphemus who remained blind, or Odysseus who lost all his men and had to wander for ten years, before getting home?
Click here for images of Polyphemus and Odysseus.