Has anyone else ever noticed how amazingly similar this song is to Pachelbel's Canon? If you put them in the same key you get:

Pachelbel's Canon: E B C#m G#m A E A B
Basket Case: E B C#m G#m A E B

It's really weird, no one believes me until I play them both for them, but if you listen to them back to back it's an uncanny similarity. Coincidence? I think not...

"Basket case" is also slang for someone who has become effectively worthless; they are mentally, emotionally or physically crippled to the point that they cannot function.

The term originally was slang for someone who has had all four limbs amputated. The derivation of the extended meaning from this should not be hard to see.