There's a saying: "treat others like you would like to be treated."
It amazes when I see cruise passengers (guests, if you prefer) treat cruise servers or other staff as if they were mechanical robots, not acknowledging them, not saying please or thank you, or some equivalent display of civility, but treating them as if they are a different class of people than themselves. I find that much of the enjoyment of a cruise is getting to know and interacting with the staff. It's worth the time when passing an employee scrubbing away at the stairs or the deck, to learn a bit about where they are from, how long they have worked on the particular ship, etc. A cruise is so much more fun when you know the staff by their names and get to greet them when you see them each time.
Many of these crew members have left their family to take a position on a ship in order to support that family, ensure proper care for their elderly family members, or ensure a better education for their children. If if they have taken a position for the adventure of working on a ship, they are still away from their family, friends and the village, town or city they grew up in. They really don't need or deserve rude treatment from "entitled" passengers. Seems to me, since we are the fortunate ones able to take cruises, that we should be at our very best when interacting with the people working on the ships.