trainspotter

n. person who collects the numbers of railroad locomotives as a hobby; intelligent but boring person (Slang)

A railfan or rail buff (American English), railway enthusiast (Australian/British English), or (often with a more specialized meaning, described below) trainspotter (British English), is a person who is typically strongly interested, in an amateur capacity, in railroads. Railfans can be found worldwide. Railfans can also be retired career railroaders who still share a love for watching trains as well.
See more at Wikipedia.org...

slang. คนที่ใส่ใจกับรายละเอียดเล็กๆ มากเกินไปจนน่าเบื่อ