In the classic American children's show Spongebob Squarepants, one line in the theme song goes like this:
If nautical nonsense be something you wish
and it is then followed by the chorus.
My question is on the use of the word be in this context. Although it could simply be a form of silly, "pirate-speak" to be entertaining, I am wondering if this could be a form of the subjunctive. The sentence is asking if you might want to watch a show about hi-jinks in in the ocean (hence the phrase "nautical nonsense") and so thus is a hypothetical and in my understanding, hypothetical statements are supposed to be used with the subjunctive.
So, is this proper English grammar, or simply a sentence intended to sound funny? If it is proper grammar, then why has this usage largely disappeared?