At the ice cream store on main street.
The only Tongans I saw laughing are the school children. In their beautiful uniforms, they are flowers in a bleak landscape.
I wish I had taken many more pictures in Tongatapu, so I could tell you many more stories. If you go there yourself, be prepared that you are going to a Third World country. All of the other islands I saw, Tahiti and her sister islands, the Marquesas, the Cooks, and Niue, they are all more beautiful, cleaner, more able to provide decent accommodations for tourists. Tonga has issues that run deep in the locals populations' psyche.