Complex sentence: Irish, short-tempered and more impulsive than intelligent, Beck and Fitz take an instant and very strong dislike to each other, and Beck never misses an opportunity to mock and dismiss Fitz's insights, even when they are proven correct.
Split into simpler sentences: Irish, short-tempered and more impulsive than intelligent, Beck and Fitz have very strong dislike for one another. Beck takes every opportunity to mock and dismiss Fitz's insights, even when they are proven correct.