Usually after I get penetrated in the anus, I experience constipation/incomplete evacuation feelings - indicating that there is inflammation in my anal canal. But when I got penetrated roughly in the anus, I ended up passing out blood and the incomplete evacuation feeling disappeared.
Someone on another Web forum said that the only time they experienced anal fecal odor was once when they got penetrated in the anus for a very long session. And I have heard from other people saying that their anal fecal odor began after anal sex or after THEY* forced something into their anus. So it could be that inflammation has something to do with our anal fecal odor because before I began to experience constant anal fecal odor, people used to complain about fecal odor only after I got penetrated in the anus, and those comments would disappear by the next day.
I heard a lady complaining on the radio about her coworker sometimes coming to work with a fecal smell from her anus, and she wondered what the coworker normally engaged in at home.
So I guess inflammation and bad bacteria are the main culprits for our condition. I have a family member who suffered from hemmroids and the person would begin to smell constipated anytime this family member felt constipated. I guess the bad bacteria increased during the constipation causing the smell to appear - alongside the fact that this family member may be inflamed internally, causing the constipation in the first place.