N. Korea is like that weird kid in your neighborhood who everyone liked to stare at but if he even so much as flinched, you'd all run away screaming

The most recent example of North Korea flinching/flexing? Threatening South Korean passenger planes flying near DPRK airspace while the US and South Korean conduct military exercises (Key Resolve and Foal Eagle).

Korean Air and Asiana Airlines have rerouted their planes to stay clear of North Korean airspace. My immediate response: You mean you were flying us near North Korean airspace?! Followed by: "Whiskey tango foxtrot?!"

Perhaps nobody at Korean Air recalls flight KAL 007. (In case you're too lazy to follow that link, it was shot out of the sky by the USSR military in 1987 when it strayed into Soviet airspace near Sakhalin, killing all 269 aboard. 

At Marmot's Hole, commenter Won Joon Choe (who is very astute on Korea issues, by the way) quotes the Joongang Ilbo as saying that South Korean planes already pass through North Korean airspace, for a fee (€685). I'm not sure on which flights that is, but I'm guessing that it would be charter flights to North Korea and perhaps flights Vladivostok and elsewhere in the Russian Far East. (The KAL 007 flight was coming from Anchorage, Alaska, a stopover on its way from New York City, so I suppose some flights headed to parts of North America or northern Europe might be shortened by taking a short cut through the DPRK.)

As the article says, North Korea shooting down a civilian plane would likely lead to full-scale war, which would be very, very messy for anyone within artillery range but would ultimately end in defeat of North Korea, with the Pyongyang government eliminated. 

Even if it doesn't shoot one down, the mere threat is a big no-no. While the US called North Korea's statement "distinctly unhelpful," the South Koreans went a bit further:

Threatening civilian airliners' normal operations under international aviation regulations is not only against the international rules but is an act against humanity. The government urges the North to immediately withdraw the military threat against civilian airliners.

Nice to see that the Lee administration equipped the Unification Ministry with some cojones. During the Roh administration, the Unification Ministry seemed almost to be a proxy for Pyongyang. 

UPDATE:

The Korea Times has printed a map of North Korea's territorial airspace, which I discuss here.

[left: Time Magazine's rather inaccurate contemporary depiction of the KAL 007 attack. Under horrific conditions, the passengers survived for some minutes after being hit.]