I'm sorry you had a difficult experience, but allow me to point something out...
Maybe this is assuming too much, but why do you think the CNAs should have said hello to you? Our teachers drill this into our heads all the time: we are students, and therefore liabilities...not assets. No one should be kissing the floor I walk on. When I was working as a CNA, I barely had time to pee and eat...let alone go introduce myself to all 10 practical nursing students. If I got to work with one, awesome. If I didn't, I wasn't about to go out of my way to make them feel all special. I just didn't have the time.
If I had a patient who was allergic to peanuts and I gave them a peanut butter sandwich, could I just shrug and say it isn't my fault because I didn't know? You took an NPO patient into the lunchroom. Why did this not strike you as a problem? If the person had eaten lunch, they may not have been able to have surgery they might have needed and it would have been your fault for not noticing they were NPO.
I found that by losing my naive sense of entitlement to kind and fair treatment, and by proving to people I was serious about my work and school, no one picked on me. Never play the meek card. If someone has a problem with you, resolve it. Don't let yourself be the victim, and you'll never be one.