A transliteration of the words "barbecue sauce" and "mustard."
When these ingredients are combined, they form a sauce that is excellent for hot dogs, bratwursts, sandwhiches, etc.
Hey, when are you going to mix up some more bastard sauce?
male ejaculate, but more specifically, ejaculate that creates a bastard child.
"the condom broke and i got my bastard sauce all up in her vag"