No one seems to have mentioned sorting, so I will.
Several different times, I've discovered that someone had hand-crafted a bubblesort, because the situation "didn't require" a call to the "too fancy" quicksort algorithm that already existed. The developer was satisified when their handcrafted bubblesort worked well enough on the ten rows of data that they're using for testing. It didn't go over quite as well after the customer had added a couple of thousand rows.
