Breaking social norms can make you a hero or an outcast. Many people admire individuality, and sometimes breaking a small social norm can get you noticed. For example, I heard on the radio about a trend called "coning" where people eat an ice cream cone upside down, cone first while holding the ice cream. Apparently this became a social phenomenon.
Sometimes the consequence of breaking a social norm is that you break a law. Laws are frequently developed around social norms. There are laws that govern hate crimes. These are based on social norms that prejudice, discrimination, and ugly behavior motivated by these are socially and morally (and what are morals but social norms?) unacceptable. If you go against these, more than likely you'll go to jail.
While it is true that breaking social norms has no legal recourse and that social norms do change with time, there certainly always exists and has existed consequences for breaking social norms. I think the blanket answer is that the person is ostracized from society. Historically this was a literal removal or banishment of the person from the socially geographically. At worst those who couldn't or wouldn't conform were banished and at best forced to live literally on the fringes of society (the edges of towns or cities).
Today while the ostracization may not be geographical it is certainly still the consequence. When you break social norms, people stop associating with you. You may lose your job. You may be kicked out a homeowners association or other group. You end up alone, ostracized because society is not comfortable with your behavior and therefore wishes it to go away.
In terms of events that "break" social norms and how people will react to them, each circumstance is different.
For example, allowing cell phones in restaurant, when it began, was a break with the social norm. Most people would go out to dinner to relax and enjoy a meal cooked away from home, and often the companionship of friends. Loud and rowdy drunks were frowned upon, as were screaming children and rude and/or obnoxious groups of people...generally in a nice restaurant (as opposed to a fast-food place). However, now people bring their cell phones with them. The phones may ring continuously or conversation may be so loud that it makes it difficult to enjoy your meal. I have seen and heard about different reactions. Some people ask to be moved to another location; some people will leave the restaurant and not order dinner. Sometimes, people find the behavior so unbearable that they say something to the other diner.
Another situation we have seen are the no-smoking laws that have been enforced across the country. This has been very difficult for smokers, who may have tried to quit or find smoking relaxing. For those of us who do not smoke, it is a relief, but it creates a struggle on the part of smokers. Some smokers have reacted with anger and frustration.
If you are looking for a potential problem within society, tell a nation that guns are no longer legal, or abortions are banned. The uprising would be fierce and furious. People feel very strongly about some things. The nation is already divided on these two issues, but changing the laws to favor one stance over another would result in wide-spread protest, and perhaps even violence.
Looking to the past and our country's decision to make slavery illegal ripped the country apart and caused a war: it needed to be done, but it divided not only the nation, but families as well. When young men started to be drafted into the Vietnam War, there were nationwide protests, young men and/or their families moved to Canada to avoid going to war, and the nation was divided as to the necessity and the ethical reasoning to become involved in that particular "war." This, too, destroyed families and turned the public against the government.
All of these examples provide instances of broken social norms. I believe that you could write a paragraph about any of them, if you have knowledge of the difficulty (some background/research) so that you can support your position with specific examples to promote your viewpoint.
You may want to write a persuasive essay, if your teacher wants you to convince him or her, or an informational essay which reports the facts. See the links provided for more information to these kinds of writings for essays.
Social norms are shared expectations about what kinds of behaviors are and are not acceptable. These are not actual rules because you cannot get in actual legal trouble for breaking them. However, breaking social norms can make people very uncomfortable and can hurt the social lives of those who do it.
For example, there is no rule against members of the same sex walking down the street holding hands. However, in my small town, anyone will get a reaction from people who see them. This leads people who do that (I have only ever seen it a couple of times) to get stares from other people and to have others avoid them.
As another example, an acquaintance of mine likes to tell groups (even if there are people who are not close friends of hers) too many things. I was at a play group for our kids with her and she told us all about how her second child was conceived in the back of their minivan in a park. This was, as people say, "too much information." By acting in this way, she tends to incur social sanctions and people often avoid engaging in conversations with her.
Breaking social norms does not have any legal consequences, but it can have a major impact on a person's social life because it can make people very uncomfortable being around them and can mark them as "weird" and different.
You will encounter the true arrogance of mankind. You will be mocked, ridiculed, humiliated, harassed, ostracized and there will be threats made against you. You'll lose friends and sometimes family. They will conspire against you, so that you have difficulty earning a living for yourself or your family. They'll slander your good name without hesitation and will delight in doing so. You might be physically assaulted. In some places, they'll murder you with stones. The most incredible aspect will be their grotesque sense of entitlement to judge others, almost as if the group was God Himself. They will break laws, violate your privacy and stalk you and feel it is not only just and deserved, but not enough of a punishment...that is if they don't kill you. So the question is, do you choose peace and love, or hate and fear.
Normative behavior is what is required to maintain the cohesion of society. Since the social norms are usually not legally binding, there may be some temptations to violate them. But unless a person is placed under very pressing circumstances or social conventions/expections border on the tyrannical/absurd, social norms should be observed for the collective health of the society.
If you are somehow inclined to break the social norms, be prepared for criticism, opposition, even ostracization. If by breaking the time-tested norms you are causing some damage to other members of your society, it is better to restrain yourself. Socialization is a very complex disciplining process which may appear as bothersome, and even detrimental to individual interest/preference. By breaking the social norms you will distance or isolate yourself from the society, and the society shall invariably hit back at a rebel.