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faddist; follow-the-crowd type; poser; trend junkie; sheep
ミーハーだと言われても気にしない。
I don't care if people call me a trend chaser.
彼女はかなりのミーハーだ。
She's quite the fad follower.
ミーハーな性格で新しいものにすぐ飛びつく。
With a faddish personality, I jump on anything new right away.