A person who collects paperclips can be referred to as a "paperclip collector." This hobby falls under the broader category of collecting office supplies or ephemera. Collectors may appreciate various designs, materials, or historical significance of paperclips.
A person who collects beetles is a coleopterist.
Bibliophile
a strawber.
collecter
A cravatologist.
supernatural
A car collector?
A paper collector
a button collector
A badge collector.
A gem collector
If you need the answer to the joke it is "a watchman"