noun
aberrant behavior; escapade; acting out
Figurative use of 'derailment act'; describes behavior that deviates from expected norms, often in a social or moral context. Can range from mild eccentricity to serious misconduct.
彼の脱線行為には周囲も呆れている。
People around him are fed up with his aberrant behavior.
会議中に突然
Suddenly starting to sing during a meeting is a complete escapade.