T-shirts are known for their comfort, but they also can be fashionable with the right proportions. A T-shirt armholes that are too large will give you the bat-wing effect. This is not only not stylish, it also might be a cause for embarrassment if waving hello means exposing parts of your body you don't want expose. If you are altering your T-shirt, take a few steps to decrease its armhole size and save yourself from overexposure.
Turn your T-shirt inside out and press it with an iron.
Use a seam ripper to remove the collar and sleeves from the shirt. Your T-shirt will look like a collarless tank top.
Put on the shirt inside out. Pull up on the shoulder seams until the armholes hit under your arm at a comfortable place.
Have a helper pin along the excess material at the shoulders to mark new shoulder seams. The armholes will change as you raise the shoulders.
Remove the shirt, being careful not to stick yourself with the pins. Sew along the pinned lines with a zigzag stitch. The new seam should run parallel to the old shoulder seam.
Cut away any excess fabric from the shoulders. Use an overlock stitch on your sewing machine to finish the raw edges of shoulder seams.
Lay the shirt on a flat surface. Line up the top of the sleeves with the top of the armholes. Trim the bottom of the sleeves, parallel to the original sleeve seams, until it is 1/4 inch larger than the armholes on the shirt.
Place the sleeves on a flat surface. Pin them along the two raw edges and sew 1/4 inch from the edge with a zigzag stitch. Use an overlock stitch to finish the raw edges of the bottom of the sleeves.
Fold the sleeve seam over at the hem of the shirtsleeve. Use a hand-sewing needle to place three tacking stitches at the edge of the hem to keep the seam folded over. This will keep the seam from irritating your arm when the sleeve moves.
Line the sleeves up with the armholes of the shirt. The side seams of the shirt should line up with the bottom seams of the sleeves. Pin right sides together to attach the sleeves to the armholes. Use a zigzag stitch to sew the sleeves to the armholes.
Line up the raw edge of the collar with the raw edge of the neck hole. Pin right sides together 1/4 inch away from the edge. Sew the collar to the neck hole 1/4 inch from the edge.
Turn your shirt right side out and try it on. The armholes should now be more comfortable.
Raising the shoulders will shorten the T-shirt.