Although all of Odysseus' encounters were dangerous, his meeting with the Cyclops was the most horrifying. The Cyclops is having Odysseus' men for breakfast, lunch and dinner.
Odysseus knows that it is matter of time before he will become the Cyclops's favored meal. This encounter proved to be the most dangerous in terms of losing his men.
Of course, some may argue that Odysseus faced the most danger when he sailed away from Calypso on his raft because it broke apart due to a storm sent by Poseidon. In this instance, Odysseus was all alone.
He had none of his men left to support him. He was floating on one piece of board and then, only then, did he cry out to the gods for help. When he admitted that he needed the gods help, he was rescued. However, this was a dangerous point in Odysseus' journey home. Had Athena not come to his rescue, he would have drowned and that would have been the end of Odysseus.
Although each encounter had a dangerous situation, there is nothing as horrible as being all alone on the ocean, not knowing if you are going to live or die. There is strength in numbers, and there is something comforting knowing you are not alone. Odysseus did not have his men for consolation. He had to go it alone.