I've had a lot of uncomfortable showers in my lifetime, but the one I just took wins the prize.
I mixed the temperature as normal, turned on the spray, and got lathered up. And then the temperature went haywire.
I don't know what my roommates were doing in the other bathroom, but it meant a wild swing to freezing that lasted long enough to require a remix. Then a wild swing to scalding, again long lasting enough to make me readjust.
I'd step out of the stream the way you do when someone flushes a toilet in a dorm or barracks, but each change went on much longer, only to swing once more once I was getting wet again.
I would have just got out. But I was all lathered up. And my scalp really needed a treatment. It could not wait.
Thankfully I have a CON of about 16. So it's ultimately okay.