Something similar happened in my job. I reported the over-engineered, completely senseless solution, after the "dev" got really angry at me about simply reviewing his code. He was gone the next week. If you have a boss, tell him when this happens. If you don't, fire him/her yourself. If the amount of complexity introduced is not worth the use cases it covers, in a business sense, then that's a review that rejects the code on that basis.