It's up to you what you do, but this is what I'd be doing. Add the buyer to your blocked buyer list before you do anything else. That stops him revenge buying if you have other things listed. As soon as the 4 days is up today/tonight, open a non payer dispute. If he then pays, it will close automatically. He might get the shirts and leave a negative and not pay. In that case, ignore it. If another 4 days passes (to the second), close the dispute. He gets a strike against his account, you get your fees back. If he leaves feedback and doesn't pay, it should automatically be removed. If it doesn't, call eBay, tell them the buyer didn't pay and the dispute is closed and they should remove it. Don't reply to it.

I wouldn't cancel. I certainly wouldn't offer to cancel. This bloke is being an **bleep**hole. Give him nothing. By cancelling, he gets off scott free, and is just as likely to trash your feedback and stars for your effort. That feedback doesn't get removed. Don't give him any power.