Cases like these I have to remiss to a time when I might have done the same thing (or something equal), and then remember I just may again do something like it again, after all I am only human. The "perfect skipper" doesn't exist (I know more than a few us think we've got that covered though). Maybe offer some assistance next time, and he won't get so close to your boat? Just sayin.
The thread was not intended to put anyone down, or say what a great skipper I am. I've made my mistakes, and have openly posted them in this forum, with the intention others might benefit.
However, the guy in the OP clearly had no plan or situational awareness, and thought he was going to motor away from the dock like a car pulling out of a parking space. Having seen several similar examples in the past, I thought I would point out what seemed obvious to me before I had ever even motored a sail boat. They don't drive like cars. Their performance (or lack thereof!) is affected by severable factors, some of them variable. All of which should be considered before casting off or docking, IMHO. If you disagree with that simple point, I'd love to see your argument. Otherwise...we don't have one.
Regarding "offering assistance"; I didn't know what he was doing (neither did he, it turned out!), and assumed he had the situation under control until it was obvious he didn't. At that point, there was nothing I could do. Fending off wasn't even an option, he was moving too fast. The only reason I noticed him at all (and saw the whole incident transpire) was because he was removing his fenders at the dock. Thought I might learn something...I didn't!
If he needed help he should have asked and I would have been happy to assist. A simple shove on his bow would have avoided the whole incident. However...it's his vessel, and his responsibly. Had he hit my boat, or torn the stern off of his, there would have be no question of that!
Just sayin (For what that worthless, passive - aggressive cliché is worth!)