the word northing has its origins from a guy named Northern. Northern is always telling over the top, crap-ass, totally untrue stories about himself and his father. "Northing" is simply another word for telling lies.
testman: "guess what!? my father and I stole 50 beers from the cops, and had to escape on a motorbike. we drove in 250 m/h!"
tz: "hahaha..your'e northing SO bad!"