Jeff is a shy and reticent person.
All extroverts are overtly expressive. People are either extroverts or introverts. If someone is an introvert, then they are shy and reticent.  No shy and reticent person likes to talk to strangers. Jeff is not an extrovert and someone who likes to talk to strangers.
∀x (Extroverts(x) → OvertlyExpressive(x))  ∀x (Extroverts(x) ∨ Introverts(x))   ∀x (Introverts(x) → ShyAndReticentPerson(x))  ∀x (ShyAndReticentPerson(x) → ¬LikeToTalkToStrangers(x))  ¬Extroverts(jeff) ∧ ¬LikeToTalkToStrangers(jeff)