Today is a slow mellow day, so today's song will be sad. LPG's I'm Sorry I'm A Noona is just such a song. I also find it to be a happy song because I know a lot of words in it.
Dongsaeng - younger person
Saranghae - I love you
Hadjimma - don't do that
Noona- older sister
bee-ah-neh (phonetically) - sorry (informal)
Abbsa (spelt wrong) - nothing/not
So basically what I understand it is saying is "Younger man, I love you. Younger man, I can't be with you. Younger man, don't come after me. I'm sorry that I'm older than you." The music video is depressing with a hopeful ending.
If you want the lighter end of things, there is also SHINee's Noona Is So Pretty...er Replay..the parody.