Farting while walking. Usually to avoid blame. Since walking creates a substantial pocket of air to in your wake, it also helps to wave your hand in front of your anus to allow the fart to escape this vortex.
While on my way to the bathroom, I was almost caught crop dusting the office. To dissipate the smell, I causally waved my hand in front of my anus to allow the fart to escape the vortex.
When someone passes gas and walks away, trailing the smell behind them. Commonly used as a tactic to avoid taking the fall of getting called out in public.