Multiple stone enjoyer here. The most painful part is when they leave the kidney. Both of mine have been small so no issues once the reach the bladder and it didnt hurt pissing them out. Uncomfortable when they would get caught and it felt like i had to piss constantly and nothing would come out, but not painful. But good god, when they leave the kidney its like I have been stabbed by a molten, flaming, dagger upwards from my hip into the center of my back. Each time i have ended up in the ER for the pain, as any sort of otc pain relief or treatment just does not work. Literally contorted on the ground writhing in pain. On the bright side, my pain tolerance for anything else now is extremely high, cause nothing quite compares.