They pronounce it as if it were spelled "kewpon." It's not. It's spelled "coupon."
It's from the French, I believe, but that is neither here nor there. I cannot think of another word in English or indeed in any other language that has the "ou" diphthong pronounced as "yew." That's just not the way that diphthong works. It makes an "oo" sound. Unless it makes an "ow" sound.
I hasted to point out that these are people who undoubtedly pronounce "duke" as "dook," so the "kewpon" thing is not only incorrect and asinine but also inconsistent.
Is there something about words and phrases that begin with "coup" that just makes brains blow a gasket?