It's a term used to describe basically any noun and can be used negatively or positively. It is everything and nothing.
Ex 1
Guy: My dad took my phone away yesterday.
Girl: Oh no. That's so bonkdakk.
Ex 2
Guy: Man, this girl the other day was being a total bonkdakk.
Ex 3
Parent: What the bonkdakk is bonkdakk?!