Like a shoehorn that guide's one's foot into a shoe, a donghorn is a man who diligently works to assist his fornicating friends in their quest for sexual intercourse.
John is always helping his friends get laid; he's a true donghorn.
A Humangalong Dongalong (hu-mun-guh-long donga-long) is another word for a joint, spliff, doobie, etc. and is largely considered as one of the most fun things to say
Hey Otto, wanna strap up another humangalong dongalong?