re: What is the origin of the "live in your parents' basement" joke?

Well, most parents just assumed when Junior went to college he was gone for good, so they converted his bedroom into something useful, like a guest room for Grandma.
Now that he moved back in, Junior is still useless and leaves dirty clothes and Taco Bell bags everywhere, so Mom and Dad don't want to see that crap in the main part of the house.
Hence banishment to the basement.