If there was one phrase I could snap my fingers to make unutterable forevermore, it would be “why don’t you just …?”1
Someone is talking about a problem, or an achievement, or an idea, and the inevitable dismissive smartass pipes up and asks “Why don’t you just (move to a different apartment / adopt / rewrite it in Rust / eat more vegetables / mount your FTP account locally with curlftpfs, and then use SVN on the mounted filesystem)?”
“Why don’t you just?” is so second nature in my old field, physics, that XKCD made a comic about it: “So why does your field need a whole journal, anyway?”
“Why don’t you just?” means “I’ve thought about what you said for five seconds and I’m so smart that I really believe what I came up with in those five seconds is more valuable than whatever YOU thought of.”
“Why don’t you just?” means “I don’t trust you to do your own thinking.”
Sometimes “Why don’t you just?” even means “let me show you how smart I am by asking you why you didn’t just do something that I know won’t even work, and make YOU explain it to test if you’re as smart as me.”
The only possible answer to “Why don’t you just?” should be “If I could just, then I would just.”
…most of the time.
The tricky part is that sometimes, “Why don’t you just?” is the right question to ask, with the wrong wording. When you’re guiding people who are inexperienced at something, sometimes they do miss the obvious, easy solution. Or even experienced people miss it sometimes.
In those cases, how do you help them out without insulting their intelligence? Because “Why don’t you just?” is all about “me smart, you dumb”. The key is to put aside your ego and accept that this time, you may not get a chance to show that you are smart. First of all, check whether it is really the right time and place to give criticism! It might not be. If it is, then it’s a great rule of thumb to assume that they already tried the obvious thing you are about to suggest. That way, if they didn’t think of it themselves, they feel flattered and can save face. And if they did think of it or try it already, then you allow them to shine by explaining their thought process. Try something like “The way that I might have solved that problem is X. Would that also work in your situation?” Or “Stop me if you tried this already, but the way I’d have tackled it would be X.”
So, why don’t you just stop saying “why don’t you just?”
 Well, actually, I’d probably pick well, actually ↩