Okely Dokely, this is a bigun so if you're interested, it's going to take a minute to load all these SUPER HELPFUL
Mark the fabric, mostly all of the markings are to denote the fly. The only other thing is for the split at the side hem. Then sew the two front pieces together at the crotch curve or what looks like the smile.
Next comes the folding of the fly portion. Left side fold to line and then fold to second line, on the right side fold 1/4" in and then fold to line. These are the fly and fly facings.
Turn fabric so that right sides are together and stitch 5/8" from the top, then turn right side out and press.
Place the front and back pieces right sides together and sew side seams, leaving open the portion for the split at the hem. Press. Then go back to the top fly area and fold the top edge 5/8" down all the way around the top and press.
Mark the fly 7/8" from the edge on both the right and left sides. Place these markings on top of one another and you have the center front. Divide the waist into fourths from this center front point. Marks won't be at side seam or center back so don't freak.
Cut your 1 1/4" elastic to the measurements according to the pattern and divide that by fourths as well. Then place the elastic inside waist 1/8" down from top edge and with the ends under facings. Match the waist markings with elastic markings and pin in place.
Stitch across elastic down the right front fly, close to the folded edge. Do the same thing on the left front except stop 1 1/2" from the bottom of the facing edge. Then stitch across elastic at the three spots where it meets the marks on the fabric.
Stitch elastic to waist 1/4" from the top edge and again close to the inner edge of the elastic. Stretch elastic to fit waist as you're sewing.
This close-up photo at the sewing machine is to show you how to finish off the center front waistband. You are to overlat the left front over the right front and stitch through all the layers. you are making a 2" rectangle. Sew over the stitching that is already there and put your needle down to turn sharp corners for the rectangle.
To finish the fly, you'll need to fold the ends under and press.
Turn it right side out and mark that semi-triangle shape and stitch through all layers. Then stitch front to back at crotch seam.
The hem is of course the final step, I like to do a nice mitered hem on these. First I fold in a triangle shape on the hem and press then I fold the hem in to meet itself at the corners. I stitch on the inside so I can see what I'm doing and I do a bar tack at the top, where the side seam meets the split. Plus I press, press, press like a madwoman. I hope this makes sense (hence the many, many photos).
Ta-dah! Boxer shorts demystified. I hope this doesn't get on anyone's nerves because it's too photo heavy and I hope someone finds it useful. Good luck!!