The quote in the photo always makes me think of the line from Patrick Swayze in Road House (I'm sure this line alone will date me) where he's training the bouncer's and tells them "I want you to be nice until it's time to not be nice." The truth is, "being nice" isn't a bad thing, but sometimes "staying nice" can be.
Remember, "being rude is relative", and just the same for being nice. Don't let your assumption that we should always be nice to everyone, all the time, lead you into an unsafe situation. Your safety is way more important than someone's possible briefly hurt feelings. If you're uncomfortable, either remove yourself from the situation and/or let the person(s) know. And remember, if all else fails, don't be fragile like a flower. Be fragile like a bomb. 💣