My opinion for three things of characteristics Thai people is
1.Mai-pen-rai - Thai people be considerate and who always the word "Mai-pen-rai". The present have many people types If say mai pen rai consequently , used to be the situation to avoid being exploited.
2.Bun and Baap - Thai people believed in bun and baap then , they must be taught child to good person. The present each family teaches children to fear sin.
3.Sanook - Thai people who enjoys every things , easy smile and friendly from the past. The present , they are still smiling at each other , be thoughtful and helpful.
For reason I choose three things : Because is things appreciable.