Sometimes I have responses to potential questions already planned out before they're presented. Usually I do not do this intentionally, but I tend to play things out in my mind involuntarily, and sometimes this yields responses that I might as well save around in my brain in case they're needed. Here's an example.
Tonight, after returning to work with my coworkers and a bag from Qdoba, a Mexican fast food restaurant, I went to the restroom to wash my hands, and since I was there, you know, pee. On my way there, I thought that if anyone looked at me funny or asked why I was taking a bag of food into the bathroom, I was going to respond "Well, it's Mexican food, so I figure it's safer to be in here already when I start eating it."
That would have been funny... to me, at least. Too bad I didn't get a chance to use it. At least these things keep me mildly amused.