I completed the quest but I still have his shorts. I can't seem to get rid of them. Any ideas?

I know this is an old post, but in case anyone else sees it, here's the answer:

Create a chest.
Put the chest in the walking path of an NPC.
Put the shorts in the chest.

NPC pathing does not go around objects. When an object is in the way, the NPC goes through the object and it is destroyed. If the object is a container like a keg or chest, all objects inside are also destroyed. You do not have to be present.

Probably the easiest one to use is Pam's route to get to the buss, but you can find images of all vanilla pathing routes.