I say it a lot when it comes to questions that are like "when did you first experience". I just draw a blank and am like "... umm always? I don't know." He actually manages to stump me with some questions - I guess I make a face when he asks one of those, and when it's followed with "I don't know?" he then re-explains what he's asking. Sometimes I say I don't know because I'm nervous, or it's actually "I don't know how to word this" or "I don't know how to answer that without thinking about it longer"... but it always just comes out as "I don't know?".

I put a question mark there because I know I tend to word it as a question. I'm not sure, and it makes me wonder why I'm not sure.

Usually those are the topics I'll end up thinking about during the week and I'll figure out the answer eventually.