Surprise reactions (mild → extreme)
진짜? (really?)헐 (whoa)대박 (jackpot/amazing)미쳤다 (insane)ㄹㅇ? (for real?)실화? (is this real life?)
Agreement (mild → strong)
응/어 (yeah)ㅇㅇ (yeah-text)인정 (acknowledged/agreed)ㄹㅇ (for real)완전 (totally)개인정 (mega-agree)
Laughing
ㅎㅎ (hehe, mild)ㅋㅋ (haha, standard)ㅋㅋㅋㅋ (lol)ㅋㅋㅋㅋㅋㅋ (LMAO)ㄱㅋㄱㅋ (chaotic laugh)죽겠다 ㅋㅋ (I'm dying lol)
The NUMBER of ㅋ matters. ㅋ alone can feel cold/sarcastic. ㅋㅋ is the minimum friendly laugh. ㅋㅋㅋ+ is genuine laughter. This is unwritten Korean social code.