The inability to properly use Excel. Most often people over the age of 40, with a strong propensity to destroy formulas. These people often use scratch paper and a calculator to overcome the burden of understanding how the worksheet operates.
CLEAR CONTENTS!!!!! My nighhand is Exceltarted, he can't grasp the concept of a formula!
when you are in an elevator and you push the button really fast over and over in an attempt to make it go faster when in actuallity you know that it does nothing.