forgetful person

(idiomatic) A piece of cake; an extremely simple thing, something trivial, a cinch, easy as pie.

朝飯前: A piece of cake; an extremely simple thing.

(telephony) a common Japanese telephone greeting: hello; used when answering the telephone / used to confirm that the person being addressed is listening, or to confirm if anyone is listening

put away

to forget / (auxiliary verb, after the continuative form of a verb) to forget to …

forget oneself / be beside oneself

slip someone's mind

slipping someone's mind

忘れな草, 勿忘草: forget-me-not