Heaping coals on his head/ to cause someone much trouble/ to heap coals of fire upon someone's head
In a sentence with a question: It hurt him. And added to the feeling of guilt that he had. It insulted him (underline the meaning of a graph).
("If your enemy is hungry, give him bread to eat, and if he is thirsty, give him water to drink, for you will heap burning coals on his head, and the Lord will repay you" - Proverbs 21:21)
Translation
Expression (Hebrew)
חָתָה גֶּחָלִים עַל רֹאשׁוֹ
Definition (Hebrew)
בִּמְלִיצָה בְּהַשְׁאָלָה: הִכְאִיב לוֹ. וְהוֹסִיף עַל תְּחוּשַׁת הָאַשְׁמָה שֶׁכְּבָר הָיְתָה לוֹ. הֶעֱלִיב אוֹתוֹ (חַתָּה מַשְׁמָע גְּרָף).
("אִם רָעֵב שֹׂנַאֲךָ הַאֲכִלֵהוּ לָחֶם, וְאִם צָמֵא הַשְׁקֵהוּ מָיִם, כִּי גֶחָלִים אַתָּה חֹתֶה עַל רֹאשׁוֹ וַ ה' יְשַׁלֶּם לָךְ"- מִשְׁלֵי כֹּה כא)