Drag your feet when you walk, climb stairs, step over roots and cobbles or chew gum.
Misspell the word 'stairs'.
Put your ski helmet on backwards... It may or may not be unsafe, but it sure looks stupid.
Put your bike helmet on backwards... Ditto.
Cut towards yourself.
Put your shirt on inside out.
Put your sweat pants on inside out.
Wear a tie in a machine shop.
Put something in your mouth, no matter how colorful, if you haven't REALLY looked at it first.
Spit it out in front of your colleagues and ask, "Are we really supposed to eat this stuff?"
When you have a really nasty cold, and you've reached in your back pocket and snagged your handkerchief, then tug at the handkerchief when your thumb gets caught in your pocket.
Loop your shoe laces under the soles of your shoes and tie them underneath.
Tie your shoes just because someone told you to.