As a brother, what should i do in a situation like this?

Im in a situation where my parents had arrange marriage to my sister with a guy who's far related to us. From the beginning of this proposal i disliked him as his behavior & character wasn't good, but my parents thought after he gets married to my sister he might change. Then recently he started arguing & raising his voice high saying that we don't give him enough freedom to get to know my sister well, like going out & stuffs. We said we cant go against our tradition & rituals and that he has to respect our beliefs. Then he immediately said that he wants to break up with my sister & that he wouldn't marry her as we dont give him enough importance, he was so rude at me when I was explaining our situation. I advised my parents that this is the right time for us to let him go. But my parents dont take my words serious, they're not bothered of what he spoke to me, they are afraid thinking that my sister couldn't get married in future as we meant them as future couples. NOTE the elders have just fixed them for each other, not registered for each other, no any ring or chain exchanging has ever happened between them. The guy isn't helpful to us in anyway, he drinks, he's a playboy type, got piercings & stuffs, being a Muslim. My sister seems like she is interested in him but one thing which im sure is that she is not matured enough to make decisions, she's just 19. I don’t want my parents to weep lifelong regretting that they gave their daughter to this guy . As a brother what would you do if your sister is going to get married to someone who is disrespectful, irresponsible & who make big decisions within few minutes?