Is it bad not to ever use conditioner on your hair if it's only 2 inches long? and can you clean your hair with conditioner only?

OK if the texture OK: A conditioner is used to change the character of hair--make it smoother, oilier, etcetera. A shampoo is to clean the hair without drying it out. That is why they are sold as separate items. With very short hair, you could try using the conditioner alone and see the consistency of your hair after a few weeks. If the consistency is fine, you can use the shampoo alone.

Conditioning ok: There is no reason not to use conditioner on hair that is only 2 inches long. Conditioner helps to detangle, moisturizer and make hair more manageable. Find a conditioner with ingredients that will work for your hair type. You can clean your hair with conditioner only, a process known as co-washing