Not sure about Tongans, but have heard stories from a friend of Japanese descent who grew up in Hawaii and was friends with a number of Samoans. If they perceive themselves to be insulted or wronged those peaceful Pacific Islanders become real bad dudes who won't stop till their honor is redeemed. They also tend to be built on the large and solid side. By reputation, they are indeed among the last people you'd want to pi** off.
The meanest, baddest most brutal rugby team I ever saw were all Samoans. They never lost. Opposing teams would start bleeding days in advance of the match in anticipation of the thrashing they were about to receive......