"Shallow and pedantic" was made popular after its use in 2005 by Peter Griffin in the episode Petarded, of the animated series Family Guy. The Griffins invite the neighbors over for game night. While they are playing Trivial Pursuit, Lois gives Peter the "Pre-School Edition" questions to let him have his moment. After winning the game, Peter becomes an insufferable bore and starts talking down to everyone. Soon, feeling smart, Peter starts picking up words and using them in completely inappropriate situations. While watching a political talk show, he picks up the phrase "Shallow and Pedantic," describing the government's efforts in the Middle East.
Later, at the dinner table, Peter says to his wife, "Now that you ask, Lois, I find this meatloaf rather shallow and pedantic."
After this episode, the phrase achieved some popularity on the internet as an amusing deprecation. However it seems most people use it without really understanding the meaning behind it, simply because Peter used it, and it sounds semi-intellectual.
"Shallow" and "pedantic" are not particularly obscure words. However, they are not words one uses very often in conversation. The combined phrase is unusual, and in modern usage, the utterance is either a direct reference to Family Guy, or an imitation of some other simliar usage seen on the internet.