80/80 is a pseudo-fad on CE whereby when a user creates a topic, and the title contains the maximum number of allowed characters (80), the topic creator posts "80/80" at the top of his or her original post. Generally, only grammatically correct titles can be considered to be true 80/80s; nonetheless, some users may bend the rules a bit or cut the title off mid-sentence to achieve an 80-character topic.
If I recall correctly, it probably appeared sometime around 2008 or 2009.
[Topic title: This topic's title is exactly eighty characters long. Don't forget any periods.] TC: 80/80 User1: Best. Topic. EVER!
[Topic title: Generally, only grammatically correct titles can be considered to be true 80/80s] TC: 80/80 User1: YOU'RE CHEATING, THAT'S NOT A REAL 80/80!!!