by all means, after you

By all means, after you is a phrase used when telling someone they can go first. By all means in this cliche is referring to the word certainly and after you in the phrase is literal. Therefore, the phrase is telling someone they can certainly go first, and is often used by individuals with good manners and want to allow someone else to go before them whether it is in line at the grocery store, or to go through the shops door first.