How about the HORIZONTALS?
I find it just as annoying when some guy gets seated next to me who can barely get his @ss between the arm-rests. That same guy usually has no concept of keeping his paravanes tucked into his sides when using knife and fork. I end up leaning half-way into the aisle to try to get clearance to eat my own meal without his elbows knocking my food off the fork and into my lap!
How about a guage like the one used to check cabin baggage for size, but designed to ensure that pax who travel in economy can actually fit into an economy seat! If they don't fit, then either make them pay for an upgrade to a seat they do fit, or seat them beside another similarly "girth enhanced" pax so the rest of us don't suffer!
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Through hardship to the bars