In terms of frivolity, it's not quite the equal of a hat with a radio on it...
...but a Jimmy Jacket still frivs a good deal.
Basically it's a giant condom that you're meant to "roll on" your beverage of choice. As you can see, the packaging reiterates the maxim beloved of health studies educators that anybody can drink a beer, but it takes a "real man" to first wrap said beer in a novelty latex sleeve.
Anyway, I am obviously not a real man because I can't get my Jimmy Jacket on. I struggled with it for a full five minutes, but just couldn't get the damn thing onto my stubby. I haven't had this much trouble since... well, never mind. But at least the beer was still there once I'd finished fumbling.