Down at the marina last evening and noticed a SR 280 DA going in circles nearing the fuel dock. Thinking there was some problem, I stood by, ready to help out if I could. As the boat got closer, I asked if everything was ok and a worried looking lady at the stern holding a dock line said "yes, we're trying to come in for gas" The captain was struggling mightly with the helm, shifting in and out of gear making sickeninig thunks as his overreved engine slammed into an unwilling transmission. I managed to grab his lines and get the boat under control. The captain seemed totally oblivious to the damage he was doing to his new boat. He then needed help with the self service gas pump but decided to fill only one tank; "they're both connected aren't they?' When I said no he replied " it does't matter, we're not going out for long". He was then met by his son and their family who loaded enough gear (beer) for a small cruise ship and proceeded to cast off. He turned the wheel hard over, slammed the boat in gear and wedged his swim platform hard into the dock producing numerous cracks in the fiberglass. I couldn't watch anymore as he waved and headed out to sea. I don't know if I'm more angry at his stupidity at taking out passengers and putting their lives at risk or watching him abuse a perfectly good boat.