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.
The sound a cat makes right at the point of expelling a lodged hairball. Usually, the lodged hairball is accompanied by a massive amount of cat vomit. Not to be confused with the hacking required to bring the hairball to the point of expulsion.
My cat blorped on the carpet! Cat: hack, cough, sneeze, choke, hack, BLORP!