Percy couldn't find any humor Penny's attempt; it was too awkward a position to be making jokes. "Well, I know." Percy said, if only because he didn't know what else to say. "No need to apologize. I hope you find what you're looking for in Charlie."
When all else fails, resort to politeness.
"I...I'd much rather not discuss this topic again, if you don't mind. It's far too uncomfortable. I mean... I don't know what to say. I don't even know what sort of closure you're looking for, or I'd give it to you."