Chest hair is a bit of a mixed bag, some people like it and others don't. However, there are some costumes which require chest hair, and sometimes a lot of it. You could buy a chest piece with fake chest hair on it, or you could make your own cheaply to apply to your chest. When store-bought, these are often made self-adhesive, but you may have to find another way with a homemade chest wig.
Measure the dimensions of the chest piece you need by holding a ruler against your subject's chest. Measure the height and width needed.
Draw a shape the size of the chest piece onto a piece of latex. Make the height width the same as your measurements on your subject.
Cut out the latex shape using the utility knife. Size it against your subject to ensure a good fit. Adjust the shape until you are satisfied with the piece.
Decide which side will be the front and which will be the back, and lay it front up.
Trim some curly locks from your wig using the utility knife. Depending on how thick you want the wig to look, you will need more hair cut.
Spread some costume glue over the surface of the latex sheet. Sprinkle the dark hair onto the latex sheet until it is as hairy as you need. Leave the glue to dry overnight.
Apply the sheet to your subject using spirit gum. Lay the sheet as flat as possible on his skin. To remove the wig, use spirit gum remover.