Number one...The Carnival paperwork and website says to leave your luggage unlock for security purposes. This should be a heads-up to you that they may go through your luggage. You should not be surprised that this happens. Were any of your belongings damaged? Your room steward is in your room at least twice a day...your stuff is right there for him/her to see. If you are not hiding something, don't worry about it!!
Number two....When you saw staff talking in groups, did you say "excuse me but I have a question/need/etc.?" On the entire 7 day cruise, I never had a problem talking to staff for any reason/need.
Number three...Were you not aware that if the food is cold, you could send it back to be re-heated? And if something was "tasteless", did you order something else to eat? Only one night of the seven was dining room service less than stellar, and mentioning it to only one person remedied the situation the rest of the trip.
A lot of time, the attitude of the cruiser is the main problem. What was your attitude?