Wow this is a very good question...One of the main ways to stay calm, is to still tell yourself “so what”, in your head, although the thought just seems really scary and horrible.

For example, if you are having thoughts about killing your parents, just think to your head “eh… so what… big deal.. I got legs, I can breathe, the weather is great”… and just skip along and have a happy day. Be around people, that make fun of your murder thoughts, mockingly, so you even know for yourself that it is not even a big deal