While I personally would like to abstain from inanimate, this story should fit with the overall theme of jockstraps without having a darker twist. (Afternote: I had fun with this story so I do plan on continuing this at one point).
You find it odd that the pack offers a transparent jockstrap. If you have a nice ass it's great to show that off, if it comes down to that. But isn't it better to leave it up to the viewer if they see a bulge, rather than seeing you dick through some transparent plastic? You try it anyway, and notice that this one is actually a rather tight fit. Deciding against it, you attempt to pull them off with no success. It only feels like they're getting tighter when you see in the mirror that you're becoming the jockstrap! Losing your limbs and extremities rapidly until you were simply a jockstrap with thoughts and somehow sight. You didn't have real eyes in the mirror, but you could definitely see. Wishing you were normal again, you immediately see yourself in the mirror wearing a transparent jockstrap that perfectly fits your form. Then you decide to have some fun with it. You wished to be an oversized purple jockstrap and thats what you were right away. You revert to normal, get dressed, then wished to be a tiny red jockstrap. Your clothes vanished and you lay there, exactly what you wished to be. Reverting to normal, your clothes came back and you still had the transparent jockstrap. One more trick, you wished to become a famous pornstar, but that was unsuccessful. You do, however, have the ability to be anybody's jockstrap. Thinking this over, you decide the best bet is to...