Succeeded at five difficult Intimidate attempts
When you see a conversation option with (Intmidate) before it, choose that. Intimidate options are a little rarer than Persuade, so do it whenever you see one. Select five of those that end up being successful and you'll have this achievement. The four Coercion skills (Coercion, Improved Coercion, Expert Coercion, and Master Coercion) are very important for this, as is the number of skill points you have assigned to Strength.