ITT: Best/most professional ways to ask your coworker "What the hell are you thinking?!"

I'll start: "Whats the reasoning behind that?"

That is a novel approach. I didn't know computers could do that.

"Why do you think it is a good idea to do x" . See if the coworker can defend the choices they made

Convince me why this is a good idea without self-marketing?

I usually come up with a "what if.." question to point out the flaw. Or if it's simply about shitty code I will say it straight out: this will be a pain in the ass to understand in 6 months. Let's refactor, here's a couple of ideas.

You can tell people that their stuff is shit without telling them their stuff is shit. It's a skill you have to learn.

@devdiddydog <------ what he said

Between actual devs, only minimal diplomacy is needed. Just tell what you think. If you think, it is shit, say so. But don't forget to include the reasons.

ordered from most asslicking to least:

"i don't understand why are you doing it this way"

"can you explain what this is/does?"

"why are you doing it this way?"