To return a wave to someone you think is waving at you, but is actually waving to the person behind you. Usually results in embarrassment and introversion.

To wave to somebody you thought was someone you knew but really you just waved to a complete stranger. That complete stranger gives you a look of dismay not for the wave but for the enthusiasm and excitement you conveyed along with your wave.

To return a honk, or look back, to someone you think is honking at you, but is actually honking to the car behind you. Usually results in embarrassment and introversion.

When you think someone is waving to you , and you eagerly wave back saying hi just to find out the person is not actually waving to you, but the person behind you. This results in extreme humiliation , and failure to know what to do next.

Anyone who has watched the movie Cowpat would understand this. A certain type of large shit. Shannon being derived from the more literal term for the nick name "shannipoo" ie. not a cute pet name but an actual shit, and from the term Shannen Doherty Face, as a Shannon Arkell type shit is often mis-shapen and strange looking. The Arkell part coming from the slang word arch-well, which is a particularly big and well used long-drop type toilet. A shannon arkell type shit can include the brain hemorrahage through your nose shit, the lincoln log shit, the mexican food shit, the crowd pleaser, the aftershock shit, the groaner, the enegizer vs duracell shit, the liquid plumber shit, the spinal tap shit, the toxic dump, the "i think im giving birth through my asshole" shit, and often gives way for a second-wave shit. See definitions for shit and dump