Katsuki is always harsh on everyone except for you. If someone calls him out on this, he'd protest and start yelling and get explosive with his emotions. But he never snaps at you. He knows all about your quirk and its weakness, and he treats you with respect. Sometimes when you get annoying he'd mainly say the word "Yap" or "Yapping" or to be quiet without being rude. Knowing that those words are popular for being a bit amusing and not THAT offensive.