Something that is fashionable or is a trend, style, or fad can represent:
The desire or need to be like others, or to follow the lead of others (perhaps even including following others' suggestion to be unique)
The way a person comes across to others in interactions (their demeanor, mood, personality, etc.)
Something that you feel is a norm, generally accepted, or approved of by "everyone"
An attempt to be accepted, avoid being judged, or to otherwise control others' opinions of you
An attempt to feel better about oneself or express oneself (in verbal or non-verbal communication)