https://www.youtube.com/watch?v=Kj0Y3iAGJbY 4:06 knock much?
https://www.youtube.com/watch?v=Q3UWjluRLus 21:54 it's polite to knock.
https://www.youtube.com/watch?v=J75EN8kVaUs 0:55 dad, you're supposed to knock.
https://www.youtube.com/watch?v=SUe728gcogM 1:04 please knock. it's habit.
参考リンク
http://bridge-english.blogspot.jp/2014/02/blog-post.html マナーがなってないを英語でなんと言うか?