What should you never do with a metal comb when cutting hair?

Using a metal comb on wet hair without proper care is essential to avoid potential damage to both the hair and the comb. Wet hair is more fragile and susceptible to breakage; therefore, using a metal comb in such a condition can increase the risk of pulling or tearing the hair, leading to split ends or further damage.

Additionally, metal combs can conduct heat, which may not be suitable if the hair has been styled or treated with other products. The comb may also lose its effectiveness if not used correctly on wet hair, possibly leading to difficulties in achieving the desired cut or style.

The other choices present scenarios that are generally acceptable. Using a metal comb on dry hair can be perfectly fine, and it's also acceptable to keep a metal comb in high humidity as long as it is dried properly afterward to prevent rust. Using it with hot styling tools can be appropriate as long as the stylist is cautious about temperature control and the specific properties of the comb being used.