I frequently have to ask other customers to reach something for me. I'm not exactly short, I'm 5'4" and I have long arms, but with my back problems, I can't stretch to reach things on higher shelves, or bend over to get things off lower shelves.
I can't imagine helping someone when they're as rude as some of the people mentioned.
I usually say something like "Excuse me, may I borrow your height for a moment?", or "You look very strong. Betcha can't lift that bag of dog food into my cart." I'm probably not being nearly as clever as I think I am, but if it makes them smile and they help me, I count it as a win. Of course, effusive thanks are always offered.
So is that rude on my part? Should I only ask for help in a formal way? Or is asking for help with a joke ok?