noun
person who gets carried away easily; person easily elated by praise; person who readily chimes in
Describes someone who quickly becomes excited, overconfident, or overly agreeable when praised or caught up in a mood. Often used in a mildly critical or teasing way. The prefixed form お調子者 is also common.
See also: お調子者
彼は調子者だから、褒めるとすぐに天狗になる。
He's the type who gets carried away easily, so if you praise him he immediately gets a big head.
あの調子者は、みんな
That guy who gets carried away easily starts goofing off as soon as everyone laughs.
Compound of 調子 (tone, condition, mood) and 者 (person). The exact historical derivation is uncertain, but it likely arose from the idea of someone whose mood or behavior changes easily with the situation.