Well, have you ever wondered why are these young (or in some cases not so young) women and men on board the flight. For most of us, they are here to do the service, and be there for our every little request. Try again, these are highly trained people, they spend five weeks doing initial training in Safety and Security Procedures, First Aid and Fire Fighting among other subject and then have periodic training to stay current.
Their main purpose in life is to make sure that the passengers remain safe and secured and finally well served with a smile.
So next time you travel don't bring on board carry on luggage that weighs more than your checked baggage and expect them to lift it for you (there is a reason why not, if one hurts their back and have to be offloaded passengers may have to be offloaded to stay within the rule of 50 passengers per Cabin Crew/Flight Attendant);
or sneak to the toilet for a cigarette and set smoke alarms or God forbid start a fire;
or horse around and be unruly (trust me they will restrain you)
Try to make their life a little easier and they will do their best to keep you safe and secure and mostly happy.
They are your Angels in the Sky.