I always felt like Patrick, having really nothing to do, though somehow conveniently having a bunch of money probably just got it from somewhere. The royalty aspect of this theory is really the only probably explanation for Patrick's lack of skill and decent income. He very likely inherited money, which explains why he simply does whatever he wants without consequences. In some ways, this could very well explain certain characteristics, like why he acts like such a pompous jerk sometimes to everyone, which could be a result of his spoiled upbringing. On the surface it seems like just a basic theory that easily explains one of the plotholes of the series, but looking deeper into it, you can really find it intertwined with Patrick's personality.