I like the 'humor' approach, too. I also think that some may 'unshun' when they want/need something from you. If that is the case, I would also let them know...
"Oh. So, now that you need money (or whatever) it's okay to not 'shun' me. How convenient. Well, I've got news for you. My wallet/purse is 'shunning' you."
Turn it into humor - and make them squirm. Another example...
{jw friend approaches and starts talking like nothing has ever happened}
{you - putting ear to purse} "What's that?" {talking to purse} "You're right!" {talking to jw} My purse just reminded me that you were shunning me recently, and doesn't think that I should be talking to you."
Something like this may appear ridiculous... and it should. Perhaps they will 'get the hint'.
Regards,
Jim TX