When Someone discriminates against someone who has ginger hair, or drinks ginger beer/ale to the extreme. Cases have been known where gingers have been placed in a ring, and have a shouting contest at each other. This is known as Ginge-bating. Being called Ginger can also be seen as an insult, and is usually shouted to someone who is not ginger.
"Hey! He's got Ginger pubes!!!" is a good example of Ginger-ism