While this video appears to be somewhat staged, it is still worth a view to watch someone try and land with their pants down.
Miles Mortensen appears to have his leg straps inside of his pants which leads us to believe that he was in on this gag. The pants wouldn’t have of come down with the straps on the outside.
While in freefall his fellow skydiver, Garren, see an opportunistic moment and makes a dive for the legs and manages to get Miles’ pants down to his ankles before whisking off with a grin on his face.
Probably what wasn’t expected by Miles is how the air temperature and wind speed makes for a nice wind chill on his exposed legs. He complains that “It’s freaking freezing”. Furthermore, his efforts fail to return his pants to their full upright position and instead rips them so that he run upon landing.