Generally such behavior is not triggered by a single event. Rather, it derives from a combination of elements of the parent/child interaction, including the child's fundamental temperament and the parents' behavior.
My sister used to stuff like this when we were kids. I think she did it out of frustration. It was a way for her to control situations. Regardless of what my parents did to punish her she kept on doing it. She had a hard time expressing in words what was bothering her or what she wanted. Some kids bite, she used to pee and poop.
At one point my parents finally decided to move me out of the bedroom we shared and put her in the smallest bedroom by herself and only placed a bed in there. No toys no tv. Instead of showering her and changing her each time she pooped at home my mom let her sit in her own mess for a day or so. She cried and cried, my mom made her clean herself up (supervised of course) and then gave her a bucket to clean up the mess each time she pooped on herself and clean up the bed and change her own sheets and clean up the floor. We were about 7 yrs old. Eventually she stopped pooping on herself. But I think she found that my mom was not caving in and that my parents were still in control that she finally gave up.
Why does behaviour happen like that? Can it be triggered by one specific event or is it the parenting style in general?
Why does behaviour happen like that? Can it be triggered by one specific event or is it the parenting style in general?
No, this behavior should not be ignored. It invites a systematic program of limit setting and discipline. Ignoring it will not help.