I think they both love talking to each other like that ..Antara likes teasing Raghu by talking starightforward to him and she says thanks only when she feels like lol ...
same goes for Rahu...he thinks if he will talk softly to Anatara ...what will happen to his tough bhai image...
they both are so fond of each others rudeness...but yes Raghu has fallen for Antara and Anatara yet has not ...she will take time ...she is super tensed and cant think of falling in love ...