You see, I don't believe that a person can say that he/she is happy but cannot bring him/herself to smile or laugh. Although, there are really some that can laugh and say they are happy but they are actually not. The magic is in the eyes of a person. We surely can smile even if in times of weakness and troubles, but that smile will not reach the eyes. Picture this: a still face with parted lips, that is all there is.
So next time your seatmate, friend, sibling, parent, nephew, niece, and just anybody else smile at you, look deep into the eyes and see if that smile reaches the eyes to know its sincere. If it is, that means that that person is happy to see you and be with you. If not, either there is something wrong with that person or you are that 'something wrong' in that person....