My wife sometimes flips out over a trivial issue, which used to confuse me when I was first married. Nowadays I know that there’s almost always some other issue that is upsetting her and the trivial issue is mostly unrelated.
The most common thing is transference. People are frustrated about issues that are difficult and take out their stress on issues of little importance.
Low and high blood sugars can cause people to react differently than they normally do.
All sorts of metabolic and physiologic disturbances can affect mood - from anemia, menorrhea, some electrolyte or hormonal imbalances including thyroid. Some infections can as well but have other symptoms.
Some psychiatric conditions are also associated with inappropriate anger. Other times, mothers may simply feel their children are already hyperactive and should avoid things (sugar, red colouring) that were commonly reported to worsen that. Or be worried she has to wash more clothes when she does not want to.
It can also be a reaction to certain medications.
In mid-2020 I found myself stomping my feet and my voice reaching octaves I didn’t know it had as I was yelling at my 5 year old over some minor infraction I don’t even remember now. I considered this entirely out of character and did not like that I could be that way. Pandemic stuff and my wife being ill for months simultaneously just added so much stress into my life I just couldn’t handle the little things with equanimity any more.
Fortunately both those stressors have subsided in the intervening years and I have returned largely to my calm and restrained former self.
This experience taught me sympathy toward people who just seem angry all the time. Maybe they’re just sick. Or tired. Or stressed. Or all three.
Certainly there are specific diseases both mental and physical that can lead to outbursts. But it can also be as simple as general stress or lack of sleep.
Nah, that’s just an average Saturday night at the Golden Corral:
Stranger
I had an aunt who had 5 kids and was perpetually pissed off over it. She kept it bottled up but then the least stupid shit would set her off.
When I was real little I actually thought people were held together with hardware as my Pop would routinely comment about how my aunt had a screw loose.
I’ve suffered from depression for nearly almost all my life, contemplating suicide as young as 5 or 6.
I used go into wall banging, fists and head for any reason or no reason at all, often just waking up in a bad mood.
I was on a low dose of Prozac decades ago when my ex convinced me to go to anger management. The Dr’s diagnosis was I had suffered brain damage because of the head banging against the wall and with a brick I kept next to the bed.
After about six months, the Dr. gave me two choices, stay on Prozac the rest of my life, or if I thought I could handle it knowing how it felt to be “balanced”, I could stop completely. I chose the later and haven’t been on anti-depressants since. I still feel bouts of rage welling up, but calm myself down before anything erupts.
Edit: It helped that my ex left shortly after my treatment was over, so I didn’t have as great manic/depressive moments anymore. Now I live alone and strive to walk the middle road in everything I do.
I live my life like Bose. No highs, no lows. 
I’m not sure they are necessarily connected but here are some:
- Going from being a fiercely anti-Trump voter in 2016 to a Trump voter four years later (“If Biden wins, you can forget about being allowed to go to church”) and now blasting Democrats all the time;
- Belief in strange theories, such as the one that the Moderna coronavirus vaccine makes your body a magnet for metals, and being very anti-vaxxish about the Covid vaccine in general;
- Spending around $200,000 in a secretive spending spree in the past two years - I don’t know on what things specifically (this is what my sister told me);
- Refusing to talk to my sister for about a year because she (my sister) shaved her head and my mom was mad about it, calling it unwomanly;
- Being very anti-Communist yet simultaneously watching a quasi-Communist-propaganda TV channel as a trusted news source (can’t figure why)
- Embracing some weird Taiwanese conspiracy theories of late;
- Spending over $8,000 on survival food rations during the pandemic’s first year, convinced that famine was around the corner; she also thinks that civil war or Texas secession is a realistic thing. She spends a lot of her time freeze-drying food as survival rations for the future, and bought two Glocks.
- Another incident from childhood that stands out: my mother getting angry because I said that “airliner” referred to the passenger jet while “airline” meant the company that operates the jets - she insisted vehemently that “airliner” meant the company. The semantics aren’t the issue, but rather, how unusually angry she was over a mere word definition, and how weirdly strongly she felt about it. This happened more than once (the dispute about “airliner” vs “airline.”) It was really a hill for her to die on at the time.
- Believing various religious prophecies, claims or whatnot that are not true.
Those are some of it.
For clarification, I don’t hold a grudge against her, and this isn’t meant as a diatribe at all. There are good traits about her too. It’s just that, over the decades, she’s had weird thoughts and behaviors and I’ve never been able to figure out the psychological circuitry behind it.
My doctor once prescribed Wellbutrin for minor depression.
The effect was immediate. Little things that normally wouldn’t have bothered me pissed me off, and things that would’ve been minor annoyances sent me into fits of screaming rage. Literally, I screamed and threw things. For the first time in my life, I knew exactly what the expression “seeing red” meant. My partner threatened to leave me.
All this happened in less than a week, I think I took the drug for 5-6 days, then I stopped it after my partner made the threat and got back to normal. Brain chemistry is weird.
Bipolar disorder can also account for mood swings in some people. Irritability is a common characteristic, for example.
One of the worst ever fights I had with my (soon-to-be-ex) wife was when we first moved in together, over the necessity of having two bottle openers.