These always get the middle-aged office ladies excited by your technological prowess:
* Treble clicking rather than drag selecting to highlight AN ENTIRE LINE
* Alt+Tab-ing between windows
* Double clicking the bottom right of a cell to copy a formula ALL THE WAY DOWN A SPREADSHEET
* Opening a Word document without saying 'Er...'
* Alt+F4-ing a window
* Banging your mouse up and down and swearing when your computer runs slowly
I think I need to not work in an office ever again.