Usually used when you are left out of a group and you hear that group laughing then you come over and you say Haha...Yeah. Results in a disgusted stare.
When you want someone to know that you say no to something, but want to do it extremely sarcastically. Comes from an old vine, in which a guy simply says "haha yeah man" to the camera. It is VERY important you say is sarcastically like in the vine, because if you don't, it can be misunderstood by normies as simply saying "yes"