1. Noun. A hairstyle popular in the early 1990s, sported by former Amiga Power journalists until present day. A haircut where the hair is shaved unpleasantly at the sides and combed straight up to form a "flat-top", a perfectly level snooker table smooth top sported above a pinch-face.
2. Adjective, "flat-topped" Obnoxious or idiotic behaviour, noticeably angry but lacking in self awareness or critical thought. Also the act of aggressively barracking one poorly thought out-idea ploughed into the ground along formulaic lines.
That inexplicably angry rant you are indulging in is particularly flat-topped, sir. And questioning my ability to 'understand simple English' is only compressing the flat-top'.