Put a smile on your face and relax. This is the best thing you should do when someone passes such remarks. One thing is understood if the person has the privilege or enjoy the rights to say anything like this to you, he is not a stranger to you. He should have avoided saying anything like this to you. Only mediocre people have such opinion about others who are familiar to them. In nutshell, people who call you useless are senseless. They will get habituated and keep passing remarks on others until some day an insane person cause damage to them both physically and mentally.