Let's learn about "미안, 까먹었네" and "말했잖아"

미안, 까먹었네  : Sorry, I forgot it

말했잖아 : I told you so!

ex)

A. 미안, 까먹었네 : Sorry, I forgot it

B. 몇 번이나 말했잖아. 잊어먹지 말라고.. : I've told you so many times. Don't forget

[other expressions]

- 미안, 까먹었다. (to younger people or friends)

- 미안, 까먹었네. (to younger people or friends)

- 미안, 까먹었어. (to younger people or friends)

- 미안, 까먹었군! (to younger people or friends)

- 미안, 까먹었구나! (to younger people or friends)

- 미안, 까먹었네요. (honourific by '요')

- 미안, 까먹었군요! (honourific by '요')

- 미안, 까먹었어요. (honourific by '요')

- 미안, 까먹었습니다. (formal; more honourific by '스‘)

[explanations]

* 내 : I (non-honourific word)

* 제 : I (honourific word)

* -가 : a particle makes 내 / 제 subjective after a word ends in a vowel

* 미안 : sorry

* 까먹다 : [=잊어먹다] forget

* 까먹었다 : past tense of 까먹다 by '-었-'

* 잊어먹었다 : past tense of 잊어먹다 by '-었-'

* 몇 번이나 : many times

* -잖아(요) : this expresses certainty or his insistence to carry one’s point or opinion

* About -잖아요 see this site : https://www.howtostudykorean.com/upper-intermediate-korean-grammar/unit-4-lessons-84-91/lesson-90/

example) 

(1) -있잖아 / -있잖니 : guess what : I’ll tell you what

(2) 걔가 했다고 했잖아(요) or 그 애가 했다고 내가 분명히 말했다 : I’m sure he did. / I said to you that he did

(3) 내가 확실히 말했잖아요 or 내가 분명히 얘기 했잖아요 : I'm sure I told you

* 잊어먹지 말라고.. : 잊어먹다 + -지(a connection suffix makes a verb negative meaning before a verb means negative nuance) + 말다 + -라고 + (말)했다

* 까먹었습니다 : 까먹었(the stem of 까먹었다) + -스(a suffix makes a verb more honourific) + -ㅂ니다(an honourific descriptive verb ending suffix)

* a verb + -다 / -네 / -어 / -아 : a non-honourific descriptive verb ending suffix

* a verb + -군! / -구나! : a non-honourific exclamatory verb ending suffix

* a verb + -네 / -어 / -아 / -군! + -요 : an honourific verb ending suffix

* a verb +  -습니다 / -ㅂ니다 : an honourific descriptive verb ending suffix by '스-' / '-ㅂ'