Telling Shem from Ark Angels that you've stolen her favorite bear-print panties quite literally sends her into a berserker rage which gives her super-strength.
Chun Woo from The Breaker may act like he doesn't care about Shi Woon, but if you touch his disciple you're dead. Talking shit about his master's death will also get him very mad. Also, seeing Shiho badly hurt makes Chun Woo one-hit that him.
Eventually, Shi Woon gets his own: anyone threatening his Love Interest Sae Hee.
For Elder Kwong anything related to Sun Woo clan.
Don't ever say the vice-principal has a "shitty car" or damage his car.
From Dorothy of Oz going near Mara with bad intentions is a sure way to upset Abee.
Mara doesn't like being called "Dorothy".
Haji from Hot Blooded Woman really hates being called a puppy. Since her full name, "Kang Haji", sounds like the Korean word for "puppy", she really hates it when people call her by her full name.
From Magician threatening Natasha will send the normally stoic immortal magician Edermask into a lightning fuelled rage.
Harming anybody weak or genuinely good is Rai's button from Noblesse.
Mentioning Munsu's former lover or best friend in a negative light, or praise Aji Tae, is Munsu's button from Shin Angyo Onshi.
TAL has one: don't ever try to hurt Hiljo when Haje is around. He was more than ready to murder Ja Gwi for killing Hiljo.