A C# WTF Exception. Is for exceptions that should never, ever happen. And then they do.

WTFException.cs

using System;

namespace Exceptions {
    public class WTFException : Exception {
        public WTFException(Exception ex) : base(null, ex) { }
        public WTFException(string message, Exception ex) : base(message, ex) { }
        public WTFException(string message) : base(message) { }
    }
}