Why was Poseidon so angry with Odysseus?

Answer 1

There are different versions of the story.

In Homer's Odyssey:

Odysseus and his crew had blinded Poseidon's son, the Cyclops Polyphemus and then taunted Polyphemus afterwards. Polyphemus prayed to his father for revenge on Odysseus.

In other versions, including The Odyssey movie: Odysseus had believed he defeated Troy without the help of the gods. So Poseidon wanted Odysseus to learn that man is nothing without the gods. Especially because it was he who had sent the sea serpent to kill the soothsayer who told the Trojans to burn the wooden horse.
Poseidon was angry at Odysseus because Odysseus blinded Poseidon's son, Polyphemus, who was a cyclops.