Mine was extra crazy on holidays, birthdays, anniversaries, trips... And I could have sworn, for full moons too!
I think it's anything that deviates from their normal routine. Often with all of these (except full moon

), there is added pressure on the BPD to do something or spend money (which, in my ex's case was triggering because he didn't have any money!). Plus, holidays or our birthdays put extra attention on us or others and they don't like that. For their birthdays, valentines, anniversary dates, we are doing things that reflect intimacy and they don't really do that either. A whole mess of dysfunction.