Everytime I play the game.
Last ones that I remember...well, trying to make Youmu`s first cross danmaku shoot backwards works 90% of the time for me...10% of the time I end up like this:

Needless to say, cue autobomb. Also, in IN I tend to fail on Reisen`s Visionary Tuning..."no worries, she`s gonna change the pattern any second, no need to bom- *death, last word bomb missed*...FFFFUUUUUUU..."
Of course, I feel like irredeemable noob every single time I miss the last word bomb window in IN.
But my most failtastic error was in EoSD Stage 2 Normal miniboss. Died on her kunai waves while trying to get close to her to kill her before the time limit for no actual reason. Cue headdesk. THIS. SHOULD. NEVER. HAPPEN.
EVER!