ready target; fair game
Describes someone or something that is an easy or obvious target for criticism, attack, or teasing. Often used with verbs like なる or にする.
He is always a ready target for jokes.
The politician was fair game for the media.
From 格好 (かっこう, 'suitable' or 'ideal') + の + 的 (まと, 'target'). The phrase literally means 'a suitable target' and is used idiomatically.