Rather than actually having to take his pants off and put them back on inside-out, Marty pulls out his pants pockets to fake the effect.
Earlier, we did see Marty Jr. wearing his pants inside-out, but like the size-adjusting jacket, this seems to be another example of Marty being a special case. Not all kids are wearing their pants inside-out. In fact, Marty Jr. appears to be the only kid in Hill Valley actually doing this.
Of course, nobody in our 2015 does this (on purpose). Although it would have seemed much more outlandish at the time, a more accurate prediction would have been that kids wear pants with their waistbands around their hips.
That weird practice started in prison because prison clothing often didn’t fit right. It was adopted by hip hop culture and a variety of rap artists. In 1992, the debut album of Kriss Kross showed the pair of rappers sagging. By 1995, the style had become more mainstream. Now, twenty years later, kids are still doing it.
We can only wish they wore their pants inside-out instead.
Prediction Accuracy: Failed