I believe it is an acronym for "Fresh Off the Boat", i.e. an immigrant. It's a slang term and I personally don't use it too much but have heard it used fairly often.
You are not a fob if you moved here from China at 9 years old, didn't read or speak your first word of English until then, and have no discernible accent as an adult.
No one would call a Hong Konger with a HK English accent a fob either.
Also clothing :-)