Time

Harry, Hermione, Luna, Cho, Ginny, Ron, Neville go back in time and play strip Truth or Dare with James, Lily, Remus Sirius, Severus and Minerva.
They obviously don't tell Remus, Lily, Severus and Minerva that it's strip Truth or Dare.
P.S. Minerva is the same age as the others, they're in 5th year.