tear of happiness is associated with the emotional feeling of a person who laugh to much which can cause tears in our eyes. sometimes when you received a surprise you are being happy and tend to cry because of being happy.
Tears of Happiness - A description of an emotional feeling humans go through occasionally when laughing to extreme, or when an event, action, or sensation occurs that makes someone feel over-whelmed with happiness. Such feelings can provoke moisture in tear-ducts located under your eye, similar to how being sad can make someone cry.
tears of happiness are the opposite of tears of hurt or pain. You are so overwhelmed, possibly from a marriage proposal or lottery winning, that your emotions let loose and you cry with happiness.