مَنْ هَذَا
Who is this?
If the person is already known, man hādhā can serve as belittlement: “Who does he think he is?” The grammar still resembles an ordinary request for identification.
Prior familiarity and a dismissive tone are essential clues. Addressed to an unknown visitor, the same words may be a perfectly genuine question; directed at a known figure in contempt, they have a very different rhetorical purpose.