Critisism, when people break promises/don't keep their world, invalidation, when others seem to be chosen over me, being mocked, attention withdrawls, when I think I'm not missed, being ignored, seeing/hearing terrible things going on in the world, when I'm around people I don't fit in with, certain music (songs that remind me of a period/people that I miss or a bad time in my life), etc...
Life in general can be a trigger.