Although his poles are far from the most expensive piece of equipment a skier uses, a bent one can still throw off technique on the slopes. It's a shame to throw ski poles away and buy new ones for the sake of a slight bend. However, with aluminum poles at least, that's not necessary.
Repair minor bends while out on the slope by gently drumming the pole against a rounded, solid object like a tree. First wrap the bend in a garment, like a scarf or sock, to prevent the pole from being dented, then gently and repeatedly strike the outside of the bend against the tree.
Repair more serious bends by pulling off the handle and filling the pole up to the top with sand. Fill the pole up to the top with sand and plug the hole with a strip of cloth to keep the sand trapped inside. The sand will keep the metal from creasing as you try to straighten it. A crease means "game over" for your ski pole.
Roll the pole along a flat surface such as table top to see the shape of the bend. When the bend stands out from the table press it flat onto the surface of the table and hold. Inspect the pole to see if the bend has straightened.
Use the same method as in Step 1 if pressing flat fails. If this does not straighten the pole either, keep it wrapped in a rag and place the most bent section into a vice. Position the pole so that the outside of the curve is pressed against one side of the clamp and slowly tighten the vice until the curve is pressed flat.