I shit in the shower once, one of the biggest I've ever done in my life too. It was 2 years ago. I had had a very bad perianal abscess and developed a fistula on my ass cheek, I had surgery and they slashed s giant gash in me from the fistula to my asshole, about 3 inch long and 4 inches deep and ran a plastic tie thru the hole, into my rectum, back out of my asshole and tied it together.
After he surgery, they warned me about constipation and told me to take a ton of stool softeners. The anesthesia slows down your body and makes your poop hard. So I had a huge hard turd in me and a massive wound around my ass that made pushing out poop insanely painful like shitting a knife. Not to mention the poop would move the plastic ziptie thru the wound.
I didn't shit for 5 days, became incredibly painful. Doctor gave me the choice between driving 30 min to him to do a "digital extractions' aka he scoops my shit out with his finger, vs me taking a few enemas.
I started with one, waited 15 minutes and couldn't poop so I added another and another. Finally I let out a hard little painful nug of poop. I was crying from the pain and turned on the shower to clean myself off since I couldn't just wipe shit into the hash.
As soon as the hot water hit my stomach, I felt an urge, and I couldn't get out in time. I shit a massive amount of feces into the shower, a huge mound the most shit I've ever seen in my life, it was a fucking ant hill. I used paper towels to try and pick it up and throw it into the toilet but then I just kept farting out water so I stayed in the shower until it was time to shit again and then dropped another massive pile of custard onto the shower floor.
That was 2 years ago, now I use that tub to wash my 1 year old son in.