do sit down
Please sit (as opposed to standing in a show of respect). Oh, there's no need for all that pomp, gentlemen—do sit down.
Do sit down.
Don't stand on ceremony.; Please sit down. (A polite phrase encouraging people to resume their seats after rising for an introduction or out of deference.) Tom rose when Mary approached the table, but she said graciously, "Do sit down. I just wanted to thank you again for the lovely gift." Tom:Hello, Bill. Bill (rising): Hi, Tom. Tom (standing): Do sit down. I just wanted to say hello.