[fatkam]

> "Why don't you just X?"

you are being too "polite" ... I think it can be a fair question.

[DamonHD]

If you start from the position that they are a fool with the words that you use, you are unlikely to get anywhere good.

Your colleague may be a fool, but that's not the way to learn anything useful from them, or to verify the fact.

[fatkam]

I don't think you are a fool because I ask such a question... I am honestly asking.

[DamonHD]

If yout put the word "just" in there like that then the strong implication is that it was an obvious thing to do and only a fool would have failed to try/do it. It's called a leading question. If that's not what you intend to imply then choose different words.

[fatkam]

true, I probably would not have included the word "just".. but I would still would have gave that person the benefit of the doubt