Well, .NET's garbage collector certainly springs to mind. Not exactly in a good way. You know you have something special on your hands when GitHub refuses to show you a highlighted version of a hand written C++ file (https://github.com/dotnet/runtime/blob/98984ccad55362a66b7fd...).

Other than that, I remember my mind was blown a few times while watching Jim Weirich's presentation on functional programming all those years ago (https://www.youtube.com/watch?v=FITJMJjASUs).