Leaving the office early when your boss has left early as well.
Pulling a Vinkie is best done between, roughly, lunch and 4pm. After 4 you can't really say it's a Vinkie anymore, that's just leaving early.
If you notice colleagues doing Vinkies regularly, they are probably not happy in their work. If you see them doing it smiling, they probably already have another job elsewhere.
A: Where's the boss?
B: he left already.
B: Dude, it's half past 5, too late for pulling a Vinkie!