The Wedding Car
Honeymoon in Vegas
The beginning of the movie shows us a happy wedding full of happy people. In this cinematic vision of rural Texas, they all live by a traditional moral code where the bride's saving herself for marriage. If you were cynical, you might think that people would get married only to have to sex.
Actually, you don't have to be cynical, because Rocky Horror tells us that this is exactly why Brad and Janet's friends get married. You can tell this by the side of their wedding car, which says, "WAIT TIL TONITE—SHE GOT HERS, NOW HE'LL GET HIS."
She got a wedding. He gets sex. We have to wonder if that's the same reason that Brad proposes to Janet. If so, the wedding might be off now that she isn't a virgin anymore.