How can I talk to my parents about prom?

Okay soo my parents really hate talkig about prom and I have no idea why.. I'm a junior and 17 and I really want to go to prom and my friends are making this big group and it's gonna be really fun and I'm going to be really upset if I don't get to go. Yeah there's always next yer but veryone in my grade is going this year so I want to also. My mom especially hates whenever something about prom is mentioned she's always like why is everyone in love with prommm?! and says it really rudely too and I don't know why. It's been my dream to go ever since I knew what prom was so how can I talk to them without them getting angry? And how can I convince them to let me go?