To Darken the Doorstep is when you go to someone's
home and you cast a shadow over their doorstep. It usually used to describe the action of someone you know and
haven't seen for a while unexpectedly turns up at your
home or it's something you tell an unwanted visitor not to do ever again.
Sue: "OMG, you
never guess who had the nerve to darken the doorstep this morning."
Pat: "Who?"
Sue: "Jo!"
Pat: "Jo, Jo who?"
Sue: " you know the one that coursed all that trouble at my
party."
Pat: " Oooh! That Jo,
haven't seen her around here for ages, did you invite her in?"
Sue: " No I did not! Told her to clear off and to never darken my doorstep again."