Dumb things I tend to do:

Pushing instead of pulling on a door
Pulling instead of pushing on a door
Putting the milk (lactaid) in the cabinet and the cereal in the fridge
Setting my alarm to AM instead of PM or PM instead of AM -- I actually did this yesterday and it tends to happen at least once every other month

Dumb things I did recently:
Putting a Beta tape in an HDCAM deck
Putting a tape in the correct deck and getting confused why it isn't capturing only to realize the power isn't on