Nope Nope Nope
Long Duk Dong is one big racist stereotype. He's a Chinese exchange student played by a Japanese-American actor, and he exists only to make cheap, tasteless, racist jokes at his expense. A gong sounds whenever his name is mentioned. He eats with his knife and fork upside down as if they are chopsticks.
Sam calls him "a very weird Chinese guy." Her brother is worse:
MIKE: I just hope we burn the sheets and mattresses after he leaves.
Why? Because Asian people are dirty? What, exactly, is the joke here? And furthermore:
MIKE: I gotta sleep under a Chinaman named after a duck's dork.
A Chinaman? We thought this movie was made in the 1980's, not the 1880's.
Finally, he listens to "Turning Japanese" by the Vapors in the car. We just can't even with that one.
The reason he's in this movie, as a character, is because Sam's grandparents have brought him to this country as some sort of exchange student.
GRANDMA DOROTHY: I think we can all help him assimilate.
And how do they do that? By having him mow their yard and do other bits of menial manual labor. Ick. Ick, ick, ick.
Dong ends up hooking up with Marlene, who is either a very giant student or a gym teacher, wrecking Grandma's car, falling out of a tree on Jake, getting beat up by Jake (because pawning off a drunk woman isn't enough, Jake also needs to beat up a helpless drunk man), passing out on the lawn, and getting kicked by grandma in the ribs.
The Donger and Sam have more in common than you might think. They're the same age (even though the actors are thirteen years apart). They both want to find someone to hook up with. And they both get called "retarded." Sam is called "retarded" by one of Jake's friends:
JAKE'S FRIEND: Maybe she's retarded.
And Dong is called retarded by, of all people, the police, when Grandpa Howard reports him missing:
GRANDPA HOWARD: What was he wearing? Well…he was wearing a red argyle sweater, and tan trousers, and red shoes. Hmmm… no he's not retarded.
This line is totally cringeworthy today, but insensitivity towards women, minorities, and the differently-abled clearly wasn't uncommon back in the 80's. We have no clue what happens to "the Donger" at the end of the movie, but we hope he escaped from the clutches of those horrible grandparents.