I have the same issue fairly often. (Being Norwegian.) We’re talking about three, maybe even four, different layers of meaning for a lot of words. Firstly, the commonly accepted, text-book meaning of a word. Secondly, the idiomatic use of a word in every-day expressions. Thirdly, the Internet’s adopted and often heavily revised usage of the word. And lastly, the connotations for this message board in particular.
It’s no wonder we foreigners get confused sometimes. 
In the case of meltdown, the applying internet and SDMB connotation is a tantrum where base internet survival instincts have been thrown out. (Like not indiscriminately insulting everyone, threatening with violence, legal or real-life consequences for the offending party and anyone who interferes.) This usually leads to suicide-by-mod*. We have many examples of this on the SDMB, as does any message board. Suffice to say that these are extraordinary events and the real-life equivalent for an adult would be a screaming match with his boss in the office in the middle of a meeting staffed by a lot of serious people in suits who don’t smile.
On preview, I see I left this post to cook for a while and others have come in. (I was out for a bit.) Ah well.
- Suicide-by-mod is the equivalent of suicide-by-cop.
