We've all seen the signs outside of restaurants before.
No Shirt, No Shoes, No Service.
But...
What if I walked into the restaurant without pants? I mean, I technically followed the rules.
Sure, it's implied that I have to be fully clothed to enjoy this establishment. But, if they're going list specific clothing items, why leave out such an important one?
Maybe it's an alliteration thing.
"No shirt, no shoes, no pants, no service" isn't quite as catchy. But leaving it out opens the door to someone walking into a McDonald's in their underwear.
I haven't Googled it, but I'm sure it's happened at some point in restaurant history.
When you give instructions, you can't be detailed enough. Otherwise, it's inevitable someone will find a misunderstanding or loophole.