|Must have been some party!|
Here Pippa is seen dancing the night away in just her slip and bra, while her dance partner wear just boxer shorts. I don't see anything wrong with this picture although I can see why it might cause some embarrassment to her family.
Look at the floor behind the couple, it looks like stone tiling, of the type that is laid outside on a terrace. The chances are this photo was taken in some hot holiday destination where stripping down would just be a way of cooling off.
They probably spent all day at the poolside or maybe even on a yacht at sea, wearing their skimpy beachwear, so this is tame by comparison.