It's a couple of days before a big wedding. The Bride comes up
with some bad news for her mother: she's found out that the
young stepmother of the Groom has bought the exact same dress
to wear to the wedding that she (the mother of the Bride) is
planning to wear.
The Bride's Mother tells her not to worry because she will just
go and buy another dress to wear to the ceremony.
"But mother," asks the Bride, "What will you do with the dress
that you've already bought?"
"Well," says mom, "I'll just wear it to the rehearsal dinner."