I'd have to understand more about your situation to really give any sort of advice. A few questions come to mind: 1. Do you believe what the startup is doing i

I'd have to understand more about your situation to really give any sort of advice. A few questions come to mind: 1. Do you believe what the startup is doing is worthwhile? How much of what keeps you there is just a need for a job, and how much is due to you wanting this job in particular? 2. Does his code function correctly? Is it overly fragile? Has it proved to be a maintainability problem in the past? Have others complained about your boss's coding style and defensiveness? If so, what action have they taken? 3. Have others commented on how you approach your boss in these instances? Do you seem overly abrasive? Do you stand your ground when he disagrees, or do you give in as soon as he does? If the latter, do you think you would face severe consequences if you did stand your ground? Lots of questions, but narrowing down what is important to you will help me and others give you better advice.