כֵּ֣ן יִנְהַ֣ג מֶֽלֶךְ־אַ֠שּׁוּר אֶת־שְׁבִ֨י מִצְרַ֜יִם וְאֶת־גָּל֥וּת כּ֛וּשׁ נְעָרִ֥ים וּזְקֵנִ֖ים עָר֣וֹם וְיָחֵ֑ף וַחֲשׂוּפַ֥י שֵׁ֖ת עֶרְוַ֥ת מִצְרָֽיִם׃
so shall the king of Assyria lead away the captives of Egypt, and the exiles of Ethiopia, young and old, naked and barefoot, and with buttocks uncovered, to the shame of Egypt.
Rashi on Isaiah
with bare buttocks (וַחֲשׂוּפַי), like חֲשׂוּף, and the yud is superfluous, like the yud of חַלּוֹנָי (the window), חוֹרָי, (nets), שָׂדָי (the field).
Rashi on Isaiah
buttocks Near the anus. Comp. (II Sam. 10:4): “And he cut off their garments in half, up to their buttocks (שְׁתוֹתֵיהֶם).” This retribution was due them because of Ham their ancestor, who saw his father’s nakedness and did not cover it, payment in kind.