First used in Mr. Natural Comix, circa 1968...the sound made when one ejaculates into another's mouth (in Mr. Natural's case, a Big Baby). Similar to the classic Batman onomotopoea's, such as "paff" "oof" or "spwack"...only, dirtier.
Blorp is
indicative of not a thin, mealy stream of
ejaculate, no...it suggests something grander, more
substantial, like a massive snowball of cum.