What you're describing is an evil AI, not just an unFriendly one - unFriendly AI doesn't care about your values. Wouldn't an evil AI be even harder to achieve than a Friendly one?

"Where in this code do I need to put this "-ve" sign again?"

The two are approximately equal in difficulty, assuming equivalent flexibility in how "Evil" or "Friendly" it would have to be to qualify for the definition.