Red: grammatical error

Blue: incorrect, awkward, unnatural, or unidiomatic usage

The mere word “tantrum” certainly draws conjures up in our minds the image of a child lying on the floor, in a not very passively quiet manner though.

"...image of a child on the floor screaming" <-- I think this is a much clearer and more concise version of what you're trying to say. "Passively quiet" is redundant.  

But, what about grown-ups?

This is just a nitpick; I don't know if you purposely chose the word "grownup," but I personally prefer "adult." There's nothing wrong with "grownup" (so don't consider this a correction per se), but as an adult American English speaker, I just feel like we use the term "adults" more frequently; there's almost a sense of childishness to the word "grownup," I suppose because we mostly hear children talk about "grownups" or what they want to do when they "grow up," etc. 

Can’t grown-ups afford to throw tantrums every once in a while too?

Well of course it would be considered childish for a man or a woman of certain age to drop to the ground and make unbridled random kicks along with an obnoxious sound.

"Man or woman of a certain age" -> "man or woman PAST a certain age." Personally I think this is a bit long-winded and would prefer simply "an adult" or "a grown man or woman," etc.

The word "unbridled" is typically used to describe more abstract things: i.e., unbridled passion, unbridled fury, unbridled emotion, etc. Anyway, this entire sentence just sounds very clunky: "...it would be considered childish for an adult to drop to the ground kicking and screaming."

So after serious investigation, and meticulous put together of ideas thought, I have come up with a brief of guide: “the art of throwing tantrums at this not-so-young age for adults”- an art that requires certain skills, which are summarized as follows:

1. One must never be right on the reason or cause of the tantrum, otherwise one is rather taking a stand, which is automatically disqualified for a tantrum function.

...I...wish I could correct this sentence. But I can't. Because I haven't the faintest idea what you're trying to say.

2. One ought to sulk for as long as possible, immersed in endless thoughts of resentment and resent for the whole world. Without any real reason of course.

3. Try to (pretend to?) sleep or slumber at any given time someone comes near to talk or say whatever whenever someone approaches.

4. Fast for the whole sulking period, (but don’t famish out starve because of your meaningless tantrums, we don’t want a gastritis as an ultimate result to end up with gastritus) assure but keep an ample supply of nourishment (food?) to remain concealed hidden from anyone everyone else around the house. Maybe not necessarily really nourishing but sufficient not to starve. Not necessarily nourishing (or healthy) but adequate to prevent starvation.

So two things: 1) you randomly switch to "we" (first person plural/inclusive) whereas before you were addressing the audience directly (second person); 2) gastritis is an inflammation of the lining of the stomach......I'm not aware that you would get gastritis from starving yourself...In fact, wikipedia says the main causes are alcohol consumption and use of NSAIDs. (I could be wrong).

5. If needed be, communicate with short answers, answer with a curt “yes/no,” but in every opportunity the preferred ones must be responses are “maybe, I don’t know, whatever, I’m fine”

6. Facial expressions are also a must for an effective performance (otherwise no one will notice there’s a tantrum going on)

lol

7. To break from end the tantrum, just come around pretend as if nothing has happened, feigning insanity or amnesia. If someone tries to dig(??) ask about the performance that had has just taken place, go back through the previous bullets and put in place practice any possible combination of them together the above.

Of course, by all means my advice is, just don’t throw tantrums…at all.

Hi, you're obviously at an advanced level, so here are some "advanced" mistakes I've noticed: Your writing is too verbose; two main reasons: 1) using words that serve little/no purpose (easy fix: trim these out!); 2) phrasing things in a longwinded or roundabout manner (think about how you can express these ideas in a clearer and more succinct way). On a related note, I noticed quite a few phrases that were incoherent; I think this  because you are trying to express an idea merely by gluing a bunch of words together and hoping the end result will convey your meaning. Unfortunately, this is not the case. However! The good news is, as you learn/improve your English, you'll develop a better speaker's intuition for the language and you'll gradually learn which words to use together and for which situations (for example, set expressions and idioms).

Anyway, I realize I might sound a bit harsh in my previous comments; I just want to say that I'm very impressed by your written English and your ambition (this was a long article, and you definitely took a lot of chances), which is why I took the time to comment on a lot of things that are fairly subtle. Good luck!