You want examples of bad design? In man alone we have a spine that is not dapted for either going about on all fours, nor fully upright stance. This is one reason for the ease with which we suffer back injuries. Ditto for our knees and ankles. Humans are also the only animals that suffer constipation -- because of the near-vertical layout of our digestive tract.
My favorite example: Wisdom teeth. They made good sense back when we had a longer ape-like jaw, but since hominids evolved larger craniums and smaller jaws, we've got too damned many teeth for the available space. And no, they're not there as "spares", they most often end up impacted even when other molars have been lost. They cause a wide range of serious health problems, and provide next to no benefit.
Or maybe God put them there to make oral surgeons rich...
There is that theory stating God must be a civil engineer ... because only a civil engineer would run a couple of waste lines through a major recreation area.
Are you referring to the tail bone? If you really think it is not needed, go find a doctor willing to remove yours and I will glady pay the deductable.