“A robe the king himself has worn”
have them bring a royal robe that the king himself has worn and a horse on which the king himself has ridden (Esther 6:8 BSB)
What it sounds like today
Just some fancy clothes and a horse ride as a reward.
The cultural key
The honor Haman designs is easy to read as mere finery and a parade. The point lies in the specifics: not just a fine robe but a robe 'that the king himself has worn,' and not just a horse but one 'on which the king himself has ridden.' In royal ideology these objects carried the king's own dignity; to be dressed in them and paraded on them was to be publicly clothed, for a moment, in the king's status, the highest honor imaginable short of the throne itself. That is exactly why Haman, assuming the king means him, grasps for it. The same logic lies behind designating an heir by setting him on the royal mule (1 Kings 1:33) and Pharaoh investing Joseph with his own signet and robes (Genesis 41:42). The exquisite sting is that Haman must personally robe his hated enemy Mordecai and lead him through the square in the very honor he coveted.
Recovered meaning
Wearing the king's own robe and riding the king's own horse was not mere finery but the supreme honor, publicly clothing a man in the king's status. Haman reaches for it assuming it is his, then must bestow it on Mordecai.