Comment by GreyMolecules

Being a 빠른 can put you in a slightly sticky situation, especially when combined with the strict hierarchy rules regarding honorifics (존댓말).

Typically, throughout middle school to university days, a South Korean individual is expected to use the honorific version of the language when speaking to someone older. This version involves a completely different set of vocabulary and grammar, used to show "respect to others" and sound "polite," effectively preventing one from being casual with others. Whereas a 빠른 is allowed to befriend people one year above their age and gets to use "반말" (the casual version of the language) with those peers.

A social complication can arise when two groups with a monotonic increase in age meet. Say, friend group A comprises a regular 95 and a 빠른 95. They became friends in high school and talk casually. Then there's group B, which consists of a regular 95 and a 빠른 96, who also became friends in high school. Now, when groups A and B start hanging out together at university, the 빠른 95 has to decide whether to use honorific or casual speech with the regular 95 and the 빠른 96.

The ones stuck in the middle, in this case the 빠른95, gets called "족보 브레이커", which roughly translates to "pedigree breaker".