How many times do you knock when you come in the room?
I heard that There is "protocol manners (International Standard manner)"
about the times you knock the room when coming in.
"Twice" is when you come in the toilet=so it is bad manners.
"Three times"=when you come in the husband or wife or friend's room.
"Four times"=humbles way of knock (you come in the superior or professor's room).
<source>http://netafull.net/life/035342.html (*Japanese website)
I wonder such way of manners is truly exist because I have never heard such manner expect this website. So would you tell me your country's manners of knocking?