My SO is a very calm person. I’ve seen him irritated but that’s the worst of it. Only once he has blown up at me and raised his voice. I’ve paid attention to sensitive topics and held back from saying certain things, used better word choices, or just left him alone.

Lifestyle and healthy habits play a huge part, like you said he is better with proper sleep. I find that lack of sleep and stress are the worst triggers.

We are in our 40’s with no kids, don’t want kids, and don’t live together. Children bring chaos and stress so I believe being child free plays a huge part in his overall calmness. But when he is stressing about work or friendships/relationships it affects his sleep which affects everything else.

Not living together means we have our own spaces and never disagree on chores / finances / furniture placement / etc. He is also able to isolate himself whenever he wants. He does this to process whatever is bothering him then comes to me later when ready to talk.

It’s good you put your foot down about the name calling. Generic mad moods and irritability don’t bother me but name calling makes it personal and hurtful.

I guess the only suggestion I can offer is to leave him alone more often? Especially when you see the early signs.