8oz aluminum can for drinks

"How fragile is this plastic coating?"

Like most things, the answer is: it depends.

Different commercially packed beverages have different corrosive powers on bare aluminum. As a result, the cans are made with different types of coatings.

If you want a smaller aluminum can, you might try V-8 juice. That stuff is acidic, so the cans tend to have a coating.

–B.G.–

"would stirring the hot chocolate scrap off the thin plastic coating that is on the inside of the can"?

I don't know but you'll probably be ingesting a good amount of BPA (& who knows what else) since heat causes it to leach in greater amounts.