I once held a shit in for a week. Literally 7 days. I was in the hospital and forbidden from using the toilet and using the portable bag toilet in the room with 6 others was not gonna happen so I held it in. Nurses gave me laxatives because they were concerned but I beat them too.
After finally being allowed on the toilet, I basically filled the bowl to the top and clogged the toilet. Yes, it hurt. I now know why and I'm never doing it again.
My friend poops once a week. He claims he told his doctor and they said it's "on the edge of normal." It freaks me out though. I'd feel so bloated all the time.