After borrowing my car without asking, he had the nerve to complain about the fuel level!

nerve 本义是"神经"，在俚语中引申为"勇气、厚颜无耻"的意思，常用于贬义语境表示"厚脸皮"或"胆大妄为"。 这里 had the nerve to do sth 是一个固定搭配，表示"居然有脸/胆量做某事"，带有强烈的不满或讽刺意味。