Odysseus was on his way home and was caotured by Polyphemus. The one-eyed.Cyclops ate some of his crew members. Odysseus mad a stake, set it on fire and poked Polyphemus in the eye. He prayed to Poseidon that if he was really his farther, he would make Odysseus's joruney home long and full of hardships. And he did.
Once Poseidon and Athena competed to be the patron god of Athens. Both had to present a gift to Athenians and which ever gift was more useful will be choosen to be there god. Athena gave them an olive tree. it has many uses from wood to olive oil. Poseidon used his trident to opened up a salt-water spring, which was beautiful but not very useful. The Athenians choose Athena. Poseidon was so upset that sent water rushing out to flood the plains outside Athens as punishment.