Consensual limits pushing always is tricky, as this require --in my opinion-- a sub with some awareness of the person he is and a skillful and careful domina, as well as some kind of connection between the two.

For my part, I can only think of Lady Daria at Warsaw Prison at the time.
She loves breaking subʼs psyche, make them cry without physical pain. This is one of the things I asked for my stay and it happened. I was so emotionally exhausted and upset that I cried without even knowing why. I dropped everything and yet it was so pleasant, some sort of comfort in this great distress.

I consider this experience as a limit pushed, as I would have been incapable to take it just 2 years before it happened. It was too true, too "NON-BDSM" to be easily handled.

Also, to me, that precise experience was the definition of no control at all. Crying like a baby is not something that can be anticipated like a specific practice. It's not like to politely ask for a breath play or impact limit to be pushed. The domina only manages to press the button, but everything that comes next is from your deepest inside and can't really be controlled by neither of the two. I don't know if I'm clear enough
Would be easier to say it in French!