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Anyone know of a good German translation for this term?

Going beyond the basic meaning of an item of clothing (heavy coat to keep out wind and rain, with a hood) it also denotes a person who is very enthusiastic about a particular hobby and in some cases takes it to extremes (examples: trainspotting, offshore radio stations in the 60s in the UK, football or cricket statistics). Sometimes also has a derogatory overtone.

Maybe the use of the word is derived from the necessity to wear such clothing in order to, for example, collect engine numbers on cold, windy railway stations without freezing to death.