I have an annoying habit when it comes to getting soda or something to drink. I will be playing a video game with a friend. I realize I'm out of soda, so I run out to the kitchen to get some. I pour it and then promptly get distracted by something (dog, computer, etc). Once I'm done with that. I go back into the living room and sit down to continue playing. A few minutes later I think 'wow I'm thirsty!" I go out into the kitchen get a new cup and set it next to the full one. Go and get the bottle out of the fridge and just before I start to pour remember that I had been intending to do that the LAST time I went into the kitchen and had forgot.
I do it quite often too.