A key warning given to the student during "health and safety at work" courses about being environment aware, in order to avoid bodily injury caused by tripping or bumping into an unseen object.
A distraction caused by spotting a stunningly good looking member of the opposite sex, resulting in the observer walking into a lampost, tripping over a kerb etc.
Simon: Dude, look over there! Trip hazard at eight o'clock
Andy: Wowsah! <Crash>, oowww fuck!