oddity

affectation, airs

attribute, characteristic, mark, property, trait

custom, habit, pattern, practice (also practise), way, wont

addiction

abnormality, neuroticism, perversion, weirdness

disposition, genius, leaning, partiality

bent, inclination, penchant, predilection, predisposition, proclivity, propensity, tendency, turn

attitude, character, humor, identity, individuality, nature, personality, temperament

marvel, prodigy, rara avis, rare bird, wonder

abnormality, anomaly, freak, monster, monstrosity

malformation, mutant, mutation

curiosity, peculiarity, singularity

accident, phenomenon, quirk, vagary

distortion, kink, mutation, variation

difference, disparity, inconsistence, inconsistency

error, mistake

contradiction, paradox

bohemian, maverick, nonconformist, quixote

coot, geezer

curio, rarity

freak