才さい弾はじける

ichidan verb, intransitive verb

be presumptuous; be forward; act clever beyond one's years

Describes someone, often a child or young person, who acts overly clever, forward, or presumptuous in a way that can be annoying or inappropriate. The verb is intransitive and often used in negative or critical contexts.

• あの子こはさいはじけていて、大人おとなの会かい話わに口くちを出だす。

  That child is presumptuous and butts into adult conversations.

• さいはじけるのもいい加か減げんにしなさい。

  Stop being so forward and presumptuous.