"Oldfag": site veteran, old user. Social acceptability of the suffix -fag is at most disputable; someone would argue that, in that specific context, it conveys simply "person", while someone else could argue that its homophobic meaning is still there. Anyway, you see the same suffix being attached to other adjectives, specially in the coordinate term "newfag" (newbie, noob).

Triforce: a symbol from The Legend of Zelda. 4chan users, specially in /b/, liked to prove that they were veterans instead of newbies by posting the text version of that symbol, as

 ▲
▲ ▲

because, if you simply copied-and-pasted it (like a newbie would be assumed to), 4chan would automatically remove leading spaces, and you'd get

▲
▲ ▲

instead. (The trick was to insert a non-breaking space before the first triangle. In Linux I remember doing this with Ctrl+Shift+u, a, 0, Enter.)

Funnily enough nothing screams "NEWBIIIIE!" the loudest than trying to prove that you're a veteran of the site.

Guy was roleplaying as a 4chan user.