I don't think the multiple meanings of the "I don't know" phrase are limited to girls. I know that I use it in different ways depending on the situation.
Sometimes I use it to mean "I need some time to think about it," when someone asks me about something that is too complex to answer properly off-hand.
At other times, it means that I don't feel like talking about something at the moment. This might mean that I don't feel comfortable giving out the information to the person asking, or that I am simply too tired to give a full answer.
Of course "I don't know" may mean that I honestly don't know the answer to a given question, and this is probably the most common use for me.
If someone is asking me to do something, I might use "I don't know" to indicate that I am apprehensive about doing something. About half of the time, this just means that I want them to ask me again before I will accept
.
It isn't that I'm not direct, but sometimes people ask questions that are either too personal or too complex to be answered in the context of a conversation.
Am I the only guy that does this?