Tropes are conventions used in storytelling to convey some sort of information to the audience. People Sit On Chairs don't convey any meaning -- they aren't storytelling conventions at all, they're just things that happen normally or incidentally during the storytelling. So if somebody is calling your YKTTW "Chairs", or PSOC, this means they think your idea is about as meaningful as the discovery that various different shows portray people sitting on chairs: It doesn't matter how commonly it occurs, this is something that never carried any meaning to begin with, making it Not a Trope.