Although we cannot provide an essay, as this is a personal assignment that only you can complete, we can still provide some guidance that can help you complete your work.
An example of a norm that you could break would be that of cutting in line at a supermarket. Although this behaviour is not illegal, it is frowned upon by society, and would be considered deviant.
I would chose this norm because it is easy to enact, as an experiment, and it does not have very serious consequences. Moreover, the breaking of this norm would most likely earn an intense reaction from other people as it is almost universally rejected. If I were to cut in line, it is likely that people behind me would immediately complain, and they would ask me to go to the end of the line.
The theory of structural functionalism would label my behaviour as deviant because this theory focuses on the way deviant behaviour allows us to define what is acceptable and what is unacceptable based on whether it promotes social cohesion and unity. Based on this, my behaviour does not promote unity, but in fact, gets in the way of it.