I cry often when I'm hungry, in pain, frustrated, or sick. I can't help it. It's particularly annoying when I'm in a public place. If I feel an episode coming on, I usually have to make it to a bathroom or someplace private.
It's been a long time since I had a true meltdown, though. Luckily, I tend to avoid confrontational situations and do my best to not get so overwhelmed.
One piece of advice would just be to monitor yourself closely... usually there are some warning signs before you end up feeling completely overwhelmed.
If you think the situation is getting the best of you, get up, make the hand gesture for "one minute please" (or possibly put your hand over your mouth or stomach like you're sick or you're going to throw up) and race off to the hall, bathroom, or similar private place. If you need to, express your emotions there. Pacing might help too.
In addition, I've also found that expressing "mock anger" in a mirror can also help. Like so, but more exaggerated and more comedic:
http://image.shutterstock.com/display_p ... 750892.jpg
Sometimes you end up just looking so silly that you burst into laughter. My room mate and I also used to practice silent screaming when we were feeling annoyed or frustrated. As in, screaming without much more than your breath coming out. It also looks really silly, so it might cause a similar comedy effect.
The idea being, though, is that you'll want to find someway to snap yourself out of the mood you're in. I know for me, meltdowns are caused in part by repressing emotion. So the solution for me is to express it, but not some place where it's going to get me into trouble. Find what works for you, though. If cartoon expressions don't do it, then find something that does.
I know that especially if you're in a heated argument, it may be pretty difficult to pull away from it. But pulling away might be the only way to "save face". It will also give you some time to collect yourself and formulate your argument.
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I don't suffer from insanity. I enjoy every minute of it.