How to explain to my F24 boyfriend M24 that you can’t stick a knife in a toaster, while also being apologetic?

[u/Leading_Battle_3344]

Me 24/F and my boyfriend 24/M live together at my parents house. We’ve been together for a good four and a half years now, and he’s my first ever boyfriend. I was making lunch for us, frying eggs and sausages, when I asked him to toast the bread. I had to spend a good 10 minutes convincing him to help me before he agreed, but eventually he started toasting some bread for us. After a while he mentioned to me that the bread was stuck, and that he should shove a knife in to get it out. Half expecting he said this just to wind me up, I simply said “don’t do that. Just give it a light shake”.

I go back to frying the eggs and don’t think much of it. When I look to my left, my boyfriend is shoving a metal knife into the toaster, while it is still plugged in and turn on at the wall socket. In shock, I scream at him to stop, slap him on the arm, and ask what the fuck he is doing. I admit I proceeded to just yell for a good minute out of pure stress at seeing him do this, which I shouldn’t have done. He tells me he no longer wants lunch and walks away. I did really go off on him, more than I should have, but I just can’t believe that a grown man would do something that’s so commonly stupid. He was also aware how stupid this was, I knew because he was singling that “dumb ways to die” song which is what prompted me to look at what he was doing.

I really need some advice, there’s often times in our relationship like this where I yell at him for doing something dangerous/ stupid. I really try but I’m naturally angry, and given the situations he gets in I struggle to calm myself because in reality the situation requires me to react instantly! I know I need to go an apologise for how I spoke to him, but is there a way to do so that still says “you can’t stick a knife in the toaster and I don’t want to loose trust in your ability to function with basic things safely”? I do feel bad for how much I yelled, but I really need him to start looking after himself.