Reddit top voted comments....
When someone who has been doing this a whole hell of a lot longer than you have looks frustrated or nervous.
Someone asks to speak with you somewhere else rather than just tell you immediately. (like when I got laid off)
If you are having an argument on the street and a dudes friends slowly work their way behind you. Thats a bad sign. It's about to go south.
When someone goes inside their house to get something in the middle of an argument.
You get that strange, watery feeling in the back of your throat; the universal I'm about to hurl feeling.
The locals all clear out... like before the 2004 tsunami in Thailand. All of the locals were running for their lives while the tourists just stood and watched the approaching wall of water.