Is it possible or probable that a women rubbing her breast against your arm or back is accidental? I other words is it possible that a women doesn’t realize that they are rubbing against you?
Yes, they are fully aware, but what it means depends entirely on the circumstances.
Were you in a crowded space and she was passing by you? Was the boobie brush against your back? Chest? Arm? Once in a very crowded bar, a woman trying to get to past where we were standing to where she needed to go gave me a 1 second thrill as passed me. brushing her breasts against my back. She was past me in a second. She just need to get by and wasn't going to say "excuse me" to the 20 people in her way, waiting for each one to make a path. It wasn't rude, it wasn't sexual.
I've had other incidental and sometimes accident contact with women's breasts in situations where we were bot reaching for the same thing, or going to the same spot at the same time. Purely innocent.
Was she rubbing her breasts against your arm or back while you both were just standing there? Was she talking to you, or someone behind or beside you? Was it crowded and she just felt comfortable being that close to you? Do you know each other?
Details matter. Provide some details and maybe we can help.