The literal meaning is "Five seconds from seriously losing it." It is generally a word used to describe someone who is 'on edge.' They are at the point just before having a total meltdown.
Person #1: Hey, buddy! I didn't want no goddamn mustard on ma' burger!
Person #2: You need to calm yer ass down.
Person #3: Hit the deck! He's MK5!
Person #1: (Explosion, resulting in the eatery getting leveled)
a car driven by people that want a slow rusty disappointing yet very reliable car, usually driven by balding middle aged men who claim the great diesel mileage is well worth the lack luster looks
Mk56 is a common name for a Tsundere. Those nicknamed or named Mk56 are apart of the Mk series. They tend to differ between each model number however, 56 has survived the longest so far.