Complex sentence: Lasse-Maja quickly became a notorious thief, stealing especially from rich people, his speciality being to dress in women's clothing so as to catch his victims off-guard, sometimes flirting with the men, and to aid his escapes from the crime scenes.
Split into simpler sentences: Lasse-Maja quickly became a notorious thief, stealing especially from rich people. His speciality was to dress in women's clothing so as to catch his victims off-guard (he sometimes flirted with the men) and to aid his escapes from the crime scenes.