Life isn't about happiness, you may feel sad, anger, hatred and many more emotions. You cannot explain your feeling when you're in the height of emotion. Probably, you may sad something in connection to what you're feeling. You don't have to feel bad for someone if they're telling something to you. Instead, reverse what they're doing, "be kind, even if others are not". In the first place, you know yourself and they're just an audience out there. Don't go to their level. You don't have to please everyone because it can be a waste of time. Focus on what you can do and live your life to the fullest.