The worst parts of Sepples

The standard "Streams". Its name hints at fast, intuitive interface that should simplify the Input/Output abstraction.
In reality its a template monster thats slow and extremely hard to use, beyond the simplest demo programs.

My favourite part of Sepples streams is formatter objects. Either, you have to input the correct formatter every time you print something, define an informal standard state you return to after using any non-standard format, or risk nonsense output in random places.

It's absolutely amazing how streams are not only a useless layer on top of stdio but actively harmful to any project using them. An API worthy of the likes of INTERCAL.