Hazarding a guess: A frequent theme in bullying (at least in my experience) is falsely building up an expectation of positive outcome, then pulling out the rug, while blaming the victim for having unrealistic expectations, usually with rhetoric that they are inherently unworthy of positive outcomes, so by deceiving themselves they have only revealed their compounded lack of worth.

Experience that enough and I would expect one could develop quite advanced heuristics to protect oneself from deception.

You hit the nail on the head. Building up false hopes of acceptance in order to tear them down is especially characteristic of how girls bully other girls, but boys can certainly do it too.

Same way an abused dog will flinch when you raise your hand. You recognise the signs of bad things to come. Most flinches are wrong, but if you're always quick on the defensive you don't get hurt as often.

Someone looks shifty, or pauses at just the right moment in their sentence. Or scratches their nose while trying to get you to do something, or can't keep eye contact when they usually would. If they excessively look away for a moment during a disagreement get yourself ready to block the sucker punch. Or they accuse you out of the blue of doing something that's a complete 180 of your character -- ask them straight back if they're doing it themselves.

I can't really explain it too well I realise, having edited this comment like 20 times, as I've only just started looking into it myself.