Ted pauses, actually considering that question. Now that she asks, it's actually a more complicated question than he initially figured. He doesn't really have any big secrets or anything like that, and there's not that many things he wants to keep private from Joan.

He wonders what she might have deduced about others before to make her worry about his reaction now though.

"I dunno," he answers honestly. "I guess... I think it'd bother me more if you made some connection about me, but then never asked me about it. You know? I'd like to have the chance to share stuff with you. Give my version of it and all that."