Phrase used usually to describe someone who is a Genius and a Son of a Bitch at the same time, or in other occasions, someone who, even being a total idiot, is someone that you admire in some way

In some rare occasions, it's also used when you want to say good luck to your Best Friend in an Humorous way
it has it's origins on a Greentext from an user on 4Chan where the user describes himself playing a game with another person
Example one: Man, he just called everyone an idiot in the presentation today, but it was the most epic way to do it, what an Wonderful Bastard

Example two: Guy G: goodbye boi, i go to save country, c u never

Guy T: Goodbye, you wonderful Bastard

Example Tree: Guy D: sorry, i can't come, i'm having Chemical Exams

Guy C: oh really? sorry to hear it, goodbye, Good luck, you Wonderful Bastard *hangs up*
Get the Wonderful Bastard mug.