I know so many docile, loving, sweet, gentle, soft spoken, dedicated positive attachment parents : With bossy TERRORS. Kids will throw fits if they are allowed to. They won't if you discipline it firmly. I never scream. I never throw fits. I'm super Mellow, loving and kind. All my kids attempted tantrums OF COURSE at the normal ages. My third was a born angry rager. But no dice, it was not allowed. Did I freak out once or twice under extreme stress from a cheating ex and bankruptcy and IRS liens and raising three tiny kids alone...yes, but that's irrelevant.
It's about being a calm, loving, firm disciplinarian. Your child is not throwing fits because you are. UNLESS, your child NEVER throws fits....they're a rare, docile little zen buddha, but then you and your mate had a few big fights, and now your child is a terror...ok maybe.
Modeling nice behavior is great in the big picture over the long haul for kids with a strong foundation of self-control that has been instilled. But parents do not have to adopt a child-like persona in order to model for their kids. My parents fought, spanked us, voted, drove cars, smoked cigars, used power tools.....doesn't mean we got to..We were disciplined for tantrums and therefore didn't throw them. Same with my kids. "Back to Basics Discipline" by Janet Campbell Matson for calm, loving, effective parenting with firm enough discipline for fits.
If you feel that he is really only throwing fits because you were, then say this. "Honey, sometimes adults get really stressed and angry and yell and fight. I'm sorry. It's not nice. We'll try to do better. You're not allowed to act that way though. If you do there will be consequences."
If that's all it takes. Problem solved. But he's probably just a normal kid throwing fits. In which case, discipline it. And being good models yourself helps too eventually. But not really at 4.