Dead Age

Punks (not to be confused with Undead Punks, that's a completely different category of enemy) aren't (usually) found as part of area combat, but appear either as negative consequences of encounters, as part of camp assaults, or as part of the Desert Day area. Since the game forces you to play through Desert Day Areas 1- 10, and each area is populated with punks (or occasionally German Shepherds), this achievement is technically unmissable if you achieve any Successful ending.

Early areas, aka Woods and Highway, don't have many failed encounters leading to Punk fights, though later area, aka City and Desert, do, though by the time Desert Night opens up around Day 35, you will have unlocked this achievement simply by being forced through Desert Day first,

Keep in mind that fighting humans (including punks) is a much tougher battle than fighting undead, as humans carry firearms and thus do much more damage than your run-of-the-mill undead.

Only enemies labeled as "Punk Assassin", "Punk Avenger", "Punk Botanist", "Punk Brawler", "Punk Grenadier" or "Punk Warrior" count for this achievement.

Punk Assassin Stats
Fast: No
Immune to K.O./Stun: No
High Defense (aka needs Breakthrough): Yes
Special Abilities: Leg Shot (Debuff)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 8
Locations: Desert Day, Camp Attacks, Failed encounters

Punk Avenger Stats
Fast: No
Immune to K.O./Stun: No
High Defense (aka needs Breakthrough): Yes
Special Abilities: Vengeance (Gets more powerful on fellow enemy death)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 4
Locations: Desert Day, Camp Attacks, Failed encounters

Punk Botanist Stats
Fast: No
Immune to K.O./Stun: No
High Defense (aka needs Breakthrough): No
Special Abilities: Heal (Heal Other), Reflex Boost (Buff)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 3
Locations: Desert Day, Camp Attacks, Failed encounters

Punk Brawler Stats
Fast: No
Immune to K.O./Stun: Yes
High Defense (aka needs Breakthrough): Yes
Special Abilities: Wary Eye (Counters Melee Attacks), Fire Through (AoE)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 6
Locations: Desert Day, Camp Attacks, Failed encounters

Punk Grenadier Stats
Fast: No
Immune to K.O./Stun: Yes
High Defense (aka needs Breakthrough): No
Special Abilities: Shrapnel Grenade (AoE)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 6
Locations: Desert Day, Camp Attacks, Failed encounters

Punk Warrior Stats
Fast: No
Immune to K.O./Stun: Yes
High Defense (aka needs Breakthrough): No
Special Abilities: Eliminator (K.O.)
Priority Targeting Level (1 - 8, 1 is max, 8 is min): 5
Locations: Desert Day, Camp Attacks, Failed encounters