The moment when you attempt to fart silently in the presence of a female and a little faeces comes out.
Can also be used as an exclamation when the above situation arises, and or as an insult whereby you intend to refer to the insulted as a piece of poo that was never intended to come out of the anus.
Oh no I've just badger wack'd in front of Suzie and I need to go home and change my wide fronts.
Your such a badger wack
If your not careful I might badger wack and give it to your mum