Waistcoats, which are usually sleeveless, front-buttoning garments that resemble an abbreviated coat, are a type of vest today worn almost exclusively as formal attire. The waistcoat is worn over a dress shirt and under a suit jacket, and historically was part of a man's everyday wardrobe. In addition to formal wear, some styles of waistcoat have become popular in youth street fashion, worn over jeans and T-shirts. Make your own waistcoat to incorporate into your formal or informal style.
Take a slightly oversized non-stretch T-shirt and cut the sleeves off directly on the armhole seam, or take out the stitches with a seam ripper. Do the same to the collar piece. Discard the sleeves and the collar. At the bottom of the armhole edge on the body, make a mark 1 inch down from the opening with a fabric pencil. Extend the opening to that 1 inch, so that you will be able to comfortably fit the waistcoat over the sleeves of your dress shirt.
Fold the T-shirt in half and lay it over a double layer of the fabric you would like to have on the outside of your waistcoat. Trace around the outside of the T-shirt with a fabric pencil, then take the T-shirt away. Draw around your existing lines, 1/2 inch away to account for seam allowances, and cut the fabric on these lines. These will be the back pieces of your waistcoat. At the centre back edge of each piece, cut a 1-by-1-inch square from the bottom.
Put the T-shirt on your body and make a marking with the fabric pencil at the bottom of your ribcage. Remove the T-shirt and fold it in half. Draw a curved, concave line from the inside edge of the shoulder seam to the ribcage marking, and cut along that line. Make another marking 2 to 3 inches up from the bottom of the centre front, and one marking 2 inches to the side of the centre front. Draw a curved convex line between these two markings and clip the corner.
Place the folded T-shirt onto a double layer of your outer fabric and trace around it. Draw around your tracings, 1/2 inch away, and cut along these lines. These will be the front pieces of your waistcoat. Lay one of the front pieces and one of the back pieces onto a double layer of your lining fabric and cut around them to get the lining pieces.
Pin together the outer back pieces at the centre back seam and stitch them 1/2 inch away from the edge. Press the seams flat and trim them. Pin together the back and front pieces at the shoulder seams for both the outside and the lining. Stitch them together, then press and trim the seams. Also stitch the front and back sections together at the side seams.
Place the lining and the outer waistcoat together, right sides touching. Pin and stitch around all edges except the upper neck edge, leaving enough room to turn the waistcoat right side out. Press the waistcoat flat, then turn the raw edges of the collar between the waistcoat and the lining. Slip stitch the neck edge together by hand, then tack stitch the side seams and centre back seam through all layers so that the lining does not move around.
Create buttonholes on the left front side of the waistcoat, between the bottom of the neckline and the bottom hem curve. Stitch the buttons on the right side, matching the buttonhole placements.