"barf bowl" discourse was started by someone whose family had a designated large bowl to puke in when sick, and perpetuated by people who think this is normal/weird or fine/gross in turns.
"poop knife" discourse was, as far as I know, just one post on reddit about a knife kept in the bathroom to break up difficult turds to aid a weak old toilet in flushing, and the amusing hijinks that ensued when the knife disappeared from the bathroom and turned up in the knife drawer in the kitchen