also: まねしんぼう
noun
A childlike or informal word for someone who imitates others, often used by children or in a teasing manner.
弟はいつも私の真似しんぼだ。
My little brother is always a copycat, imitating me.
「真似しんぼ！」と子どもが友達に言った。
The child called their friend a copycat!
真似 is the general noun for imitation or mimicry, while 真似しんぼ is a more childish, teasing term for a person who copies others.
Derived from 真似 (まね, 'imitation') + しんぼ, a suffix likely related to 坊 (ぼう, 'boy') or a childlike ending. The exact origin of しんぼ is uncertain.