イチャモン (いちゃもん, ichamon) is a casual but advanced Japanese word that indicates unreasonable or nitpicky complaints. It is usually used as “イチャモンをつける”, meaning ” to give unreasonable complaints” or “to nitpick”.
Comparison to ケチをつける
イチャモンをつける is very similar to “ケチをつける”, and these expressions are basically interchangeable. The slight difference between them would be that イチャモンをつける emphasises one’s complaints are unreasonable and very picky. On the other hand, ケチをつける is more often used to describe a fastidious person nitpicking about something good and satisfactory for a majority of people. It includes, for example, complaining about the taste of water served in a good restaurant, and complaining about a gift/service one receives from someone. Another difference is that “イチャモン” can be used as a noun by itself, while “ケチ” has this meaning only in a few expressions. In fact, “ケチ” is usually used as a な-adjective that means “stingy”, and it is considered irrelevant to the idiom (although these words seem to share the same origin).
Most of the criticisms are イチャモン (unreasonable complaints), so you needn’t worry about it.
You should keep away from people who always イチャモンをつける （make non-sense complaints）
Don’t ケチをつける (make unreasonable complaints/negative comments) about others’ lifestyle
Synonyms: 文句 (complaint), 言いがかり, 難癖
Synonyms in English: nitpick, complain
Related words and phrases: ケチをつける