Don't Design Angry
If it's true the story is simple. According to David, Simon hires David to design a logo and make some graphs. Simon never pays him but asks for extra work for free. A truly hilarious email exchange ensues. According to Simon, Dave is a raving lunatic and a liar.
Seriously, this guy is epic. But I don't know if I would have burned that bridge. It sounds like he was told that the previous work was going to be paid for if the deal worked out, which it didn't. Rather than saying no I think I would have asked for money up front, including enough to justify hours lost on the other project that didn't pan out.
I mean, if this guy were to do the work without cash up front he'd be a noob. There's just not enough information there to say if he threw away a paying job or mocked some imbecile that was just wasting his time.