1.
to read the room, to pick up on the atmosphere
To sense the mood or unspoken feelings of those around you and act appropriately. A key social skill in Japanese culture.
空気読んでよ。
Read the room, will you.
Cultural note
Reading the air (空気を読む) is considered a fundamental social skill in Japan. Someone who fails to do this is called KY (空気読めない, unable to read the room), which became a popular slang abbreviation.
The particle を is sometimes dropped in casual speech: 空気読んで instead of 空気を読んで.