A word that most likely originates from the word "Fap" which is synonymous to "masturbate". To call someone a "Fappo" would then be similar to calling someone a "Wanker".
That guy is a total fappo!
War cry declared right before collision with an object. Similar to "cowabunga," "oh shit" and that George of the Jungle yell which-I'll-be-damned-if-I-can-spell-out.
The term was made famous on the internet by a photoshopped Spider-Man comic strip in which our hero mistakes an overturned truck for his long-term arch-nemesis and proceeds to assault the truck by rope-swinging straight into the side of it.
Spidey: "My doctor's retarded. I don't have a brain tumor...say, if it isn't my old arch-nemesis, a truck!"
Narr: SPIDER-MAN GIVES CHASE!
(Spider-Man swings down toward the truck)
(Spider-Man collides with truck)