Here's a conversation I had at work:

Me: "this project that I've inherited, aside from the UI problems it has, it also has severe code problems that need to be fixed"

Project Manager: "I don't care about the code. The code is not my concern. Don't waste time on it and just make the app look good."

Give him what he asked for. deoptimize the shit out of it, then get paid to "optimize" it again later.

Metaphors tend to work well:

"Ah, I should rebuild it in your image: A nice front; but no function performance, broken inside due to past mistakes, evolved into something so repulsive that it's fundamentally unlovable"

Or... compare it to quality/performance vs looks of a car or something, if you actually want to keep your job.

Non tech people are pragmatic and dont care about inner workings of an app. Car metaphor would work great, or mention the tech debt

@SortOfTested or maybe get fired because "Why the hell did you make it so slow? It was not this slow before you started! You suck!"

Sure, put a Ferrari body on a 15 year old Kia. Fresh coat of paint and some plastic parts will do wonders. I could even put a spoiler on it, just for you!

You'll hardly even notice the knocking and backfiring and the smoke pouring out of the exhaust.