1) A british soldier who faught against the soon to be Americans in the American Revolutionary war. They were called lobster backs because they wore red coats.
2) Slang for an annoying british person who is arrogant and cant stop boasting about how much better there country is than america.
Your nothing but a dirty lobster back.
An archaic slur for a British person - still used humorously today (British Army used to wear red coats - lobsters are red).
That dirty Lobster back has bad teeth.