Boundaries are a funny thing. You are told to set them up, protect yourself from harm, but then the very people who tell you to have them are the first to take offense when you say no.
"It's me. It's us."
This is always the first sign they don't care enough to actually respect the wall you've carefully constructed. When you say, repeatedly, to stop and they instead continue because they feel they are granted rights you have blatantly said they do not have.
This doesn't even have to be a physical act of pushing past the word no. I find it's usually a conversation I wish to step back from. Think on, even. Form the words that won't be misconstrued and twisted into what they want to see and hear. However, this is just a way for them to be the victim. To say "I don't know why you suddenly turned on me." There was never a sudden turn. When conversions are replayed, words are re-read, and the disregard for your space is seen time and time again. When you've said you don't have the same thoughts, feelings, or desires, but they repeatedly, publicly and privately, ignore that no, there's nothing left to say, not even good-bye.
Because to them, you were never a person with your own thoughts and needs, you were just a person they thought they could manipulate into playing their games the way they saw fit. So no matter how pleasantly you try to part, you will always be the one at fault. Because they tried—tried to talk it out, tried to tell you their point of view, tried to make you listen. But they weren't trying to have a conversation, a conversation goes both ways, has a hint of mutual respect. No, they were trying to control you and nothing more.
These little boundary pushers always end up a victim in their own eyes, and when the tides shift and the mountain of actual victims stacked up behind them seen, all they know to say is "no one told me different" because our boundaries were never part of their desires.