Learn to communicate. Be nice. Avoid personal insults and abuse. If you can't, why are you here wasting time "helping" people? Flag personal attacks, useless sarcasm, insults; don't be a spectator.
New or occasional users are really encouraged to comment!
It takes 15 reputation point to flag posts. From my understanding, not all first time users can even flag, especially with the (sometimes) close votes and downvotes they go through at the same time. The higher population seem to keep each others in check, use the flag system and downvote, and keep it on topic.
In higher population, there's more people and older users who enforce a certain positive attitude. In lower population, this is harder to achieve... It's also harder to keep in check the rebellious users because of public intimidation and coercion; some people won't defend themselves or others because it's easier to just shut up but the result of this passivity also leaves full freedom to the bad attitude of certain dominating users.
Apparently the only way to tame down the "aggressive" users is to simply flag them. (edit) When dealing with mature individuals, these below were considered unacceptable:
(eg. "You are stupid" or any "You are --insert negative word to describe a user---" or "Hello kettle, you're black" or "I know you meant XYZ, don't deny it")
Description: Committed when a person substitutes abusive remarks for evidence when attacking another person's claim or claims.
Abuse of derogatory words (same category as personal attacks)
(eg. "Your idea is stupid" or "Doing this is stupid" or "Only stupid people..." or "Your answer is overloaded with..." or "You use pointless...")
Description: A pejorative (also called a derogatory term, derogative term, a term of abuse, or a term of disparagement) is a word or grammatical form expressing a low opinion of someone or something, or showing a lack of respect for someone or something. It is also used as a criticism, hostility, disregard and/or disrespect.
(eg. "I have a car, does that make me a mechanical engineer?")
Description: Overt irony intentionally used by the speaker as a form of verbal aggression.
(eg. "My brother went shopping and...")
Description: Not on the main topic; irrelevant to the discussion.
(eg. "I see you do this everywhere and people don't like you" or bringing events from other stacks on unrelated questions/answers, pursuing an individual by bringing off-topic events)
Description: The use of force, threat, or coercion to abuse, intimidate, or aggressively dominate others. Act of harming or harassing via information technology networks in a repeated and deliberate manner. A repeated pattern of such actions and harassment against a target by an adult constitutes cyberstalking.
(eg. Giving personal information on users, posting unrelated content to attack a user, encouraging group attacks, supporting insults made by others even if irrationals, the "you vs them". And see above.)
Description: Tool that encourages online mobs to destroy the reputation and careers of people who made perceived slights.
Immature and incomplete/unclear ideas/noise or passive-aggressive comments
(eg. "...Photoshop???????" or "Relax..." or "Why are you so upset?" or "Whatever" or any short comment without any explanation or question or reasoning to help the discussion going or end. More examples)
Description: Indirect expression of hostility, such as through procrastination, stubbornness, sullenness, or deliberate or repeated failure to accomplish requested tasks for which one is (often explicitly) responsible.
A way to be great hosts is to use a productive style of communication; What the community should aim for and the opposite of the examples above. The examples above restrain communication, the examples below encourage it and make it clearer. Confusion is a waste of time.
Description: The quality of being self-assured and confident without being aggressive. Assertive communication involves respect for the boundaries of oneself and others. It also presumes an interest in the fulfillment of needs and wants through cooperation.
Description: The status, methods, character or standards expected of a professional or of a professional organization, such as reliability, discretion, evenhandedness, and fair play.
Description: Applied method of problem solving, characterized by an unbiased, honest attitude, which can be demonstrated in a number of different ways: - One's personal beliefs do not interfere with the pursuit of truth; - Relevant facts and information are not purposefully omitted even when such things may contradict one's hypothesis; - Facts are presented in an unbiased manner, and not twisted to give misleading impressions or to support one view over another; - References, or earlier work, are acknowledged where possible, and plagiarism is avoided.
Description: The state or quality of being true even outside of a subject's individual biases, interpretations, feelings, and imaginings. A proposition is generally considered objectively true (to have objective truth) when its truth conditions are met and are "bias-free"; that is, existing without biases caused by, feelings, ideas, etc. of a sentient subject. A second, broader meaning of the term refers to the ability in any context to judge fairly, without bias or external influence; this second meaning of objectivity is sometimes used synonymously with neutrality.
Description: The process of groups of organisms working or acting together for their common/mutual benefit, as opposed to working in competition for selfish benefit.
The only questions here could be: Do I make sense, do you agree with this? Can moderators give us some clues on how we can make their job easier and still have fun? How do occasional or new users feel?
Disagreeing is alright, imposing your opinions is not so don't expect people to simply comply. If you keep disagreeing with an answer, provide evidences in your own answer. If you can't, gracefully admit it and move on; no need to fight for your ego. Fallacies are never a very intelligent way to "win" an argument and should be avoided...
I do flag what I consider very bad but it seems like the definition of aggression is not the same to all of us; the Meta of StackExchange seems to share the same views as mentioned above though.
I'm not implying that the entire Graphic Design community is bad (far from this).
Interesting links about the same topic:
The NEW new "Be Nice" Policy ("Code of Conduct") — Updated with your feedback
Could we please be a bit nicer to new users?
Why do we let hostile users dictate the perception of Stack Overflow?
I don't flag - What is wrong with me?
The problem with extrinsic motivation
I haven't found a single Meta about how to flag and what should be flag in this Meta. You can search for "flag" and have a look at what you'll find...
Obviously, seeing the numbers of downvotes and upvotes on this Meta within 1 day might indicate that people seem confused about flags and maybe some mix concepts of personal disliking vs objectivity. It's also possible they simply don't agree on what most professionals define as good communication.
In all fairness, it doesn't change the fact this meta post is about what "should" be flagged or not, and encouraging people to do so. AND inviting the discussion on this, the topic, not the poster.
It simply ended up DERAILING into bringing other events that I clearly don't feel comfortable with some users (2) and one that I even had to report using the "contact us" because my flags were totally ignored. I honestly don't know if the comments were finally deleted because of this or if it's simply a coincidence. Obviously, there was some confusion on what's acceptable and what's not.
Now one could wonder why the topic here was brought back to discussing my behaviors and these issues, and almost nothing from this post! I thought these things had to be done in a private way to be fair. Or maybe this is just another "animal farm".
Then, my suggestion is to simply invite the mods to define themselves what should be flag or not, as it was very well done on the Physics stack. What's above is simply a detailed descriptions of some of the examples given there, maybe mods will do a way better job at vulgarizing this and selecting what kind of level of communication they want in their own stack since they're the ones sorting the flags (or absence of).
PS: This is clearly not about downvoting or not agreeing with techniques. This is about "how" to disagree. Downvote is there to be used.