Captain Stanley Lord
This guy already looks like a douche, and he totally was one. While he wasn’t on the Titanic, he was close enough to make a difference. He was the captain of the Californian, which was close to the Titanic when it started sending out distress calls. In fact, he ignored the calls and left it up to the Carpathia to mount a rescue. That ship was 60 miles away and it took 2 hours to get there.
If Lord decided to help, he would have arrived 10 minutes before the Titanic went down, and taken up to 400 passengers on board. considering that only 728 of 2,225 survived, he could have made a difference.
Mysteriously enough, the ships log from that night went missing, so no one really knows what happened, and why Lord ignored a distress call. Whatever the reason, it was a dick move.