What does どうだ mean?


So, I have the sentence

> 礼儀のひとつも見せたらどうだね騎士殿

I am getting stumped on the どうだ part. If I am reading the slang dictionary
correctly (and I can only find it in a non-English one), it seems to be slang
for どや顔, which I can't find in other dictionaries (although split, it seems to
mean "cheap lodging face(person)"), and then it says

> 「どうだ？」という意味で使われる方言。語尾をあげて

Which as far as I can tell, means that it is a suffix of some kind as part of
a dialect. It's not very specific, and seems to leave the sentence incomplete.
Google Translate says it means "it do".

So my understanding of this is hindered by conflicting alternate translations
and the possibility of it being dialect-specific. Can anyone get me on the
right track?

If it helps, the previous thing the character said was something like "What
sort of attitude lets you enter [my apartment] at your convenience?"

The full slang dictionary entry is this:

> どや顔（どやがお） - 日本語俗語辞書
>
> 【年代】 2007年 【種類】
> †『どや顔』の解説どや顔の『どや』とは関西方面で「どうだ？」という意味で使われる方言。語尾をあげて「どや？」と聞くこの言葉、何かが完成したり

And it highlighted the portion that matched my search.

I hope this question isn't too narrow-focused.




It's standard, normal Japanese. どう = how; だ = the copula. "How would it be if
you showed me even one courtesy, Sir Knight." But it really means, "How about
a little manners here?".




It's standard, normal Japanese. どう = how; だ = the copula. "How would it be if
you showed me even one courtesy, Sir Knight." But it really means, "How about
a little manners here?".

