expression, ichidan verb
pick a fight; find fault; complain unreasonably
Used when someone deliberately looks for a reason to argue or complain, often in a quarrelsome or petty way. The phrase implies an aggressive or nitpicking attitude.
彼はいつもささいなことでいちゃもんを付けてくる。
He always picks a fight over trivial things.
隣の客が料理にいちゃもんを付け始めた。
The customer next to us started finding fault with the food.