"Are you the king of the Jews?"

"That is what you call me."

"OK boys, the 'king' needs a crown!"

Henchmen snickering, making a crown of thorns. Not really that complicated.

Not an expert but maybe it helps you to know that Romans had all kinds of floral crowns, e.g. Caesar's laurel crown. It's a story for the citizens of the Roman empire so that could be a context to interpret it.

vindictive

he wasn't really saying he was king of the Jews, he was basically saying I Am.. And only God or the Messiah is able to make such a claim. This is why the Jewish leaders didn't try to stop the Romans from executing him for the crimes of basically saying that religion is wrong.

The Romans (at that point) weren’t concerned about suppressing Christianity as a religion, but with using the execution to deter potential independence movements. So they gave him the crown of thorns to indicate to Jewish separatists that their political aspirations would be self-defeating.