Undo within a limited short time window not a bad idea although maybe not a high priority.  I often accidentally upvote stuff as well.  Happens on reddit as well but you can simply undo your upvote at any time (not something i'd want)

EnormousPony

mikhael

bitcoin

Ask SN: What new features would you like to see on SN? 

It's easy to accidentally hit the lightning button. Losing one sat is pretty minor, but might put a little more distance between the icon and the title/comment, or give like a 10 second undo window