I can't think of a particular bug, but I encountered one database so horribly misused, so poorly configured, for which no staff was given proper training, and w

I can't think of a particular bug, but I encountered one database so horribly misused, so poorly configured, for which no staff was given proper training, and with no data sanity checks in place, such that the university department using it had lost in excess of $700K revenue through one of its services over the course of 3 years.