Marc Giusti, the chief digital officer at Leo Burnett, has found this out the hard way after discovering a fake Twitter account in his name, http://twitter.com/giustification, filled with pretentious Nathan Barley-style Tweets making him look like a self-involved gobshite.
It contains Tweeted gems such as "A good salad is like a digital marketing toolbox. Different things with a range of slightly different tastes. OMG ... is Google the lettuce?" or "It's Friday lunchtime which means whisky sour and some good old-fashioned Giustification. Praise me. I mean be."