The term ginger does not seem like it was originally meant as an insult. I personally do not think it is an insult, neither do a few red-haired people I know. It simply means red-haired person. It is ok as long as you don't say it with a negative connotation or intent to insult anyone. Gingers have feelings too!! LOL

We are more likely to use it as an adjective, not as a noun, but either way some people are offended by the word "ginger". In fact, the noun "redhead" or the adjective "redheaded" are considered more polite terms.

frankly, it really really depends.

You can use the term, "Ginger," to describe someone to a third party, but preferably not in the company of the person with ginger hair. In Ireland where ginger hair is relatively common, there is no bias towards ginger people , but in the UK it is often seen as an undesirable trait, and people with ginger hair in the UK often suffer abuse, bullying and harassment.

if you are good friends, it's no problem