Remember these things when it comes to patients:
Just smile and be pleasant. Soothe them by letting them know you don't like going to doctors or hospitals or, if you feel the person is in good enough condition then joke a little. When people feel ill they feel wounded and scared out of their minds. If you don't get a positive reaction from the patient then don't take it personally. Working in Health Care is a rewarding career when you are making people better, but until they start feeling better and their fears are put to rest then you aren't going to see the good side of them. Some people are gentle as lambs and cooperate, while others can be a royal pain in the butt.
If you are talking about coworkers (you didn't mention patient in your question) then you need to realize that miserable people usually have personal problems. Because you are a Medical Assistant doesn't mean you have to take disrespect from a coworker so stand your ground. My favorite saying is (I look people straight in the eye when I say it) is, 'What type of bug do you have up your butt today!' It's amazing that this statement shocks them, makes them think and 9 out of 10 times they start laughing or they'll apologize. People are stressed today because of over-work, including shift work, personal problems, financial difficulties. Don't take it too personally. As you get older (like me) you get a tough hide and barnacles on your butt! LOL