Losing the streak.
So... If you ever lost your streak comment below how high you were or approximately if you don't remember. I would like to see the highest person because they will get lingots because I feel bad. My brother lost his streak recently at 110 days, he quit Duolingo and had a meltdown too, his username is thomaselovespop. Don't bother trying to give him lingots or saying nice things on his profile, because, like I said, he quit Duolingo.
I just got my 100 day streak today, and I have to admit that it is pretty cool to keep a long streak, but I don't think anyone has ever joined just to have a good streak. The goal is learning a new language and being able to have a simple conversation with a native is much cooler than any streak! After all, you can't keep your streak forever (and it would be pointless to), but you can remember the language for all of your life :)
Your brother should learn that streaks aren't the main priority and they are only used to show off most of the times. If he really had a meltdown because of that, you and/or your parents should probably teach him how to control his emotions and stop being so anxious for showing off. Not sure how old is your brother (normally these kind of stuff happen to people under 13 years old), but the sooner you and your family teach him to control himself, the lesser he will have meltdowns in his life.
At least we can say he didn't really care about learning languages, hope his mind changes and returns here, just focusing on what actually matters.