Analogous to phrases such as “What the fuck” or “What the hell”. Often used in the context of describing something utterly confounding or inexplicitly stupid. Can be abbreviated to “What the dil” if children or those easily offended are present.
Sam: Whats up bro?
John: Nothing much, expect I'm building a rocketship to Mars so we can play ping pong in zero gravity!!
Sam: What the dildo??