Saying that he will report you to eBay is hardly threatening. Threatening behaviour is behaviour that merits reporting to the police.
He is unnecessarily rude and offensive, especially for a business seller, but this is something we're all liable to encounter occasionally when trading with strangers online. What probably happened is that this was a customer return which he failed to check properly before reselling. This often happens. I once bought a "new" electric razor, and found it full of someone else's hair!
In fact, you have done him a favour by not using eBay's money back guarantee because the item was not new as described. eBay would have accepted your word for the item condition and he would have had to refund you in full, and pay for the return postage.
Anyway, you don't have to worry about him reporting you - eBay won't be interested. Just forget him and move on.
