I'm unfortunately not exaggerating in my title, and looking for advice on how to address this with United--sorry for long description, just want to be accurate:

I'm flying BZN-DEN-IAD in bulkhead row of E+, and I'd planned to buy a snack box for the DEN-IAD leg for lunch since I had a tight connection in DEN and couldn't buy something. During the announcements right after takeoff, it was announced Bistro lunches and snack-boxes would be available for purchase.

I had my credit card handy, and the beverage cart came around, but I was only offered a drink (generally in my experience on UAL in E last couple of years, one FA will do the drinks, while the other will ask if you'd like to purchase food). I figured the second FA would be along, perhaps they were spacing out the services, and didn't think much of it. After another hour, I was hungry. My seatmate had already rung for an FA twice just for more water, so I thought I'd save the FAs another trip and stretch my legs, and walked back to galley to ask about a snackbox.

Two FAs were back there, and I asked the female FA if they had food any snackboxes for purchase. The male FA (who I'll call Jim here, not his real name since I'm uncertain of FT rules around that) answered instead, and said they were all out. I was surprised, so I just said "Oh. Wait, you are? Were they offered for purchase? I guess I didn't notice."

He FLIPS out, and shoves his name tag into my face. I recoiled, and said, "Sorry, I'm confused??" (I was legitimately puzzled, not trying to passive aggressively make a point). And he starts flinging open all the drawers and the cabinets in the galley, violently enough that a couple of lower plastic bins landed on the ground. And says, "See, there aren't any left!!"

Me: "Wait, I think there's some serious confusion--did you think I was accusing you of lying? I really wasn't, I'm just surprised."

Jim the FA: "Yes you were accusing me of lying about bringing them around!!"

Me: "I don't know how we got off to such a bad start here. I'm really just confused so was asking. I'm not mad, I'm not even annoyed, just puzzled. I fly United about twice a month, and it's so far been that one FA will offer beverages, and another food. I really thought I was only offered a beverage"

Jim the FA: ANGRY LOOK

(at this point I was legitimately frightened by him, and it certainly didn't seem worth pushing the point)

Me: "I really don't understand what happened here, but I'm just going to go back to my seat since I think that's best now"

Jim the FA: "GOOD, you SHOULD!!"

So I'm back at my seat, and actually shaking because this was legit scary (I don't scare easily, honestly). I never raised my voice, I never accused, I seriously just asked confused questions with a smile (at least initially) about a snack box!

I'm going to write an email to the UA Customer Service inbox through the website, but I'm wondering how best to write it and/or if other avenues are better? I have Gold status, for what it's worth (not much, I know ).