Why is it their negative attitudes effects everyone around them? I have noticed one negative attitude can pull down a whole group.. One happy person can't cheer the group up... Why is that?

We had one guy last trip that talked non stop. HIS way was the only way but his way was always the worst way to do something. He picked on one guy (the youngest of the group) non stop. No matter what story you told, he had one better. He had everybody on the boat aggervated and po'ed and pulled our light happy mood we always had on there down. Everyone was counting the day until crew change to get away from him. We are ALL praying he won't be sent back to us again.