True courtesy respects the wishes of the recipient.
Thus, for instance, if you find yourself in line to get on a bus and notice a person behind you, and you offer to let that person go ahead of you; and if that person says, "No, you go ahead, thank you," and you again offer; and if that person says, "No, really, you go ahead" through gritted teeth?
You should fucking well get on the bus, already.
Because, by continuing to insist—and even dragging in someone else in line!—you are not doing something nice for the person behind you. You are inflicting upon that person something unwanted, solely for your own satisfaction.
And that is no kind of courtesy.