カチンと来る（かちんと くる） is to be offended.

「カチンと来る」（かちんと くる）is used to mean to be made to feel upset or angry because of something someone says or does that is rude or embarrassing.

「かちん」comes from the sound that is made when you hit something like metal.

「かちん」is often written in katakana as is often the case with onomatopoeic words.