Means to have been a long time ago.
Commonly said by Green Day in the song "Whatsername" in which the lyrics "forever ago" are repeated several times.
It can also be said by stupid retards without good grammar, people too lazy to express themselves in other words, and by people who really DO feel it's been forever ago.
Person 1: Hey, has that girl you met at the DDR party called back you yet?
Person 2: Nah.... it's been forever ago; dude, she isn't calling.
Once known as TheCuzGuy, ForeverAloneYet is a devout socialist who loves to post stuff about the Soviet Union and say how good it was. ForeverAloneYet is also a master stalker who spends 90% of all his time on FANDOM scrolling down the Contributions and UserProfileActivity tabs of other users.