Esther 3:5 (ESV)

5 And when Haman saw that Mordecai did not bow down or pay homage to him, Haman was filled with fury.

Haman had not noticed Mordecai’s disobedience before. Perhaps Mordecai purposefully kept his distance or turned away whenever he saw Haman approaching. But now Haman paid attention to Mordecai and he saw that the officials had told him the truth. Mordecai refused to pay him honour. This enraged the conceited viceroy.