Longinus, in his treatise On the Sublime defines the main topic of its writing as
a certain distinction and excellence in expression.
Longinus explains that, for something to be categorized as "sublime", it must reunite traits that are hard to reach and quite complex to perform; anybody can be a writer, or a speaker, but it takes someone with a superior command of language and pragmatics to instill in the listener a sense of near-cosmic connection to the message.
To be sublime is to awake in the listening audience a transcendental experience that spark innermost emotions. The use of language is elevated not in form, but in substance and use; in not so many words, it is a mastery that is only achieved by those who truly mean to express a deep and sincere emotion through words.
According to Longinus, the effects of the sublime are quite defined. It is
to feel our souls lifted up by the true Sublime, and conceiving a sort of generous exultation to be filled with joy and pride, as though we had ourselves originated the ideas which we read
Therefore, the FALSE sublime consists on the opposite: on using flamboyant language and over-complicated discourse to merely sound as if an important point is being made but, in actuality, the message that comes out of the over-used language is empty, shallow, or inconsequential. Longinus would argue that if you, as a speaker, cannot move your audience, you are carrying on discourse unnecessarily or unproductively; the only way to convey magic behind words is by reaching that physical and spiritual range of self awareness and contemplation. Once words and their meaning are solidly combined and used by an inspiring speaker, the sublime will manifest. If the opposite occurs and all you hear are big words with no inspiration behind them, then that would be classified as "False" sublime.