The best to get this achievement is to do with Zack 'Old Man' Brooks or Ivan 'Il Fusile' Prelli, because both of them have one skill already at 4. Ones you unlocked one of them go to Heroes, choose one and buy a skill point. For Ivan it's Agility that's already at 4, for Zack it's Instinct. Buy the skill point so it's up to 5 and bleep, bloop achievement is yours.