Strictly speaking, the phrase "Jealous Much?", means "are you very jealous?", that is to say it is question rather than a statement.
By contrast, it can be turned into a statement simply by reversing the order of words. Thus "much jealous" would mean "I am very jealous".
Unfortunately, most people today have a flagrant disregard for proper syntax, and so the distinction between the two has become blurred.
However, the literature on the subject is very unambigous on the matter, and most experts consider the word order to be so important that both question marks in written work, and intonation in speech are irrelevant. That is to say, the question mark may be freely omitted from "Jealous much?" without affecting the meaning, while any stray question marks in "¿Much jealous?"are to be ignored.
Person 1: Jealous much?
Person 2: Much jealous.
Person 1: Would you care to elaborate on that.
Person 2: No.
This is a completely erroneous statement. Jealously is being protective and guarding of what you have. The desire for what others have is envy, not jealousy.
A: "Jealous much?".
B: "you mean, envious much?, fool".
A: "What? You're just jealous".
B: "You don't even know what jealous means".
Simply another way of saying "I'm so jealous"
Also can be used as a question.
Sam-I have that new game you wanted.
Jake-OMG, jealous much!
Susie-I'm loads hotter than you. Jealous much?