無作法だ

is rude

phrase Uncommon #18,093
is rude 無作法 means having no manners; だ makes it an assertion.
JA: 食事中にスマートフォンを見るのは無作法だ。
EN: It’s rude to look at your phone during a meal.

人を指差すのは無作法だ。

It’s rude to point at people.

彼の態度は無礼だとは言えないが無作法だ。

His attitude isn't exactly rude, but it is rather uncouth.

彼は無作法だが、それでも私は彼を愛する。

He is rude, but I love him anyway.

そんな事を言うとは、あなたは無作法だ。

It was rude of you to say such a thing.