It is a derogatory term used against people from the future. The term gooback came from the fact that when they travel thru the time portal a side affect causes them to be covered in goo, hence the term gooback.
I just want a double cheeseburger you fucking gooback!
Person who arrived via time portal from the year 3045 to escape the harsh conditions of that era. A blend of all present-day races and speaks a language that is a mixture of English, Turkish, Chinese etc. Tends to work for extremely low wages, displacing hard-working present day Americans. Time-traveling had left them with goo on their backs. See also wetback.
("wentback" would have made sense without the need for goo.)
"That mother-fucking gooback took my $140K-a-yearlogistics job for 90 cents an hour!"