"..he tried to work out what made the difficult girl tick"(45).
Amateur Psychoanalysis
From my experience it seems like everyone fancies themselves able psychologists capable of divining the cause behind the behaviors of everyone around them and what decisions they'd make in theoretical situations. How about you try it! Try to put one of your roommates into one of these outdated medieval personality types below.

Sanguine
Characteristics: Extroverted, a real people person, quick to anger, quick to forgive, easily distracted, optimistic, energetic.
Characteristics: Extroverted, a real people person, quick to anger, quick to forgive, easily distracted, optimistic, energetic.

Choleric
Characteristics: Extroverted, wants to get things done, leadership, full of themselves, charismatic, stubborn.
Characteristics: Extroverted, wants to get things done, leadership, full of themselves, charismatic, stubborn.

Melancholic
Characteristics: Introverted, wants to get things done, leadership, serious, organized, hard worker, may appear depressed.
Characteristics: Introverted, wants to get things done, leadership, serious, organized, hard worker, may appear depressed.

Phlegmatic
Characteristics: Introverted, likes people, lazy, awkward, self blaming, timid, insecure.
Characteristics: Introverted, likes people, lazy, awkward, self blaming, timid, insecure.