Basically, there are bad apples, seeds or whatever you like to call them in every group, in this case, South Asian guys. Yes, these particular guys probably felt entitled and superior to you and it deflated their egos that you rejected them. They might not be used to it as well. It doesn't make it right though. Forget about these people, because they themselves seem racist, not you since you are not generalising and abusing them. Racism is wrong on all accounts. Those guys were probably desperate for sex and expected you to comply with ease. It probably surprised them that you didn't, and angered them as a result.