When someone "steps out of line", it means they have broken a rule, acted inappropriately, or gone against the norm. Synonyms for this phrase include "cross the line", "break the rules", "disobey", "deviate", "misbehave", "transgress", "violate", "defy", "rebel", "challenge authority", "act out of turn", and "go rogue". Each of these words captures a slightly different nuance of what it means to "step out of line", but they all convey a sense of going against established norms or expectations. Whether intentional or accidental, stepping out of line can have consequences and may require a person to reflect on their actions and make amends.