I sewed 2 pieces together - oops wrong way - took them apart. Then I "fixed" them and sewed them correctly... or I thought I did. I re-sewed them wrong! Same sides of the fabric with the needle holes and everything. Once is understandable, but twice??
When I do hand work, I have a tendency to sew through my finger. It's just the top layer, so I don't notice and it doesn't hurt (or bleed), there's just a piece of thread running through my finger.
And my personal favorite - I was once fussing with the needle (foot up) because it was stuck on something, and to free it (which did work, btw), I put the foot down... only my finger was right there. Needle went through my finger (that did hurt, not like the hand sewing), but I did free up whatever I was trying to free.....