FWIW, I have no idea either, and the fact that there is only one Google hit suggests that it is not a well-known expression, to say the least. Practically any random combination of words scores higher than that!
I think it is just hyperbole. Having a sub-zero vocabulary is an exaggerated way of saying a very small vocabulary indeed. No hits probably because it was a coined jocularity here.
hey clive, hp u doing fine. i wud really appreciate if you let me know of a good source to learn advanced english. And how to use vocabulary in sentences. looking for your reply.
i wud really appreciate if you let me know of a good source to learn advanced english. You need to go to a good class, with a good teacher. You also need to read a lot and, if possible, speak a lot with native speakers
And how to use vocabulary in sentences. looking for your reply. As I said, read a lot. You can also use Google to try to see how words that interest yo