OK, first of all, how old are you and if you are a minor is it really obvious?Second, best way to sneak is to do it alone. Theater staff is mostly alerted to groups but lone sneaker is hard to catch unless they have a watchdog in front of the auditorium that`s playing an NC-17 movie.Third, if you manage to sneka into auditorium that`s playing Shame, don`t sit alone but where there are more people, best to be middle middle. if you sit on the side, theater checker could see that you are obviously too young.Fourth, try to look older so that when you mingle with the rest of the audience, nobody pays attention to you and go "you`re too young for this! Guards!". Don`t wear a hoody and backpack cause that screams 15 years old.