Celticmusl saidIf your ass can't fit through the window, you can't fly, it should be that simple.
OK, that gave me a mental picture that made me smile. Based on the boxes or frames that some airlines have at the gate, that if your carry-on luggage won't fit into, you have to let them take it for check baggage.
So I imagine a window-sized frame at the gate, where you have to drop trou and see if your bare ass fits. If it doesn't you don't fly, or else have to buy the adjoining seat. I like it!