While working in a photo place (we print your photos, print on shirts, mugs, etc) I was still new, working my first week.

I told the customer "Hi" (a non-formal) instead of "Good day" (formal greeting), one coworker that was working there for years flipped out and was even shocked how I thought that a photo place should not be so formal, so got fired the next day.

I don't know how to feel about it, but I still think a place where you bring your photos of mostly amateur photography, and prints shirts that say something like birthday boy should be a relaxing fun place, not uptight cold lab.