Take one standard pair of long johns.
Two lengths of elastic long enough to just go around the lower thigh (2-3 inches above the knee.
One pair of scissors.
A needle and thread or one sewing machine.

Put on the long johns and make a mark on the leg at mid-knee.
Take the long johns off.

Cut the legs of the long johns off at the mark you made.

Find your lengths of elastic and sew them into a loop just tight enough to stay in place by themselves. (Or about the tightness of a pair of flashes.)

Place the loop of elastic over the cut-off leg of the long johns.

Fold up a hem in the cut-off long johns and sew the elastic inside the hem.

You have now created KILT JOHNS.
congratulate yourself on a job well done with a wee dram.