"Inexplicably, everyone at the gym knows me as "the computer expert" even though I took great pains when I first joined to describe myself as a "tech journalist"."
Never, ever in a context like this use a term like "tech" or "engineer" or something like that. You'll be the guy that can fix everything, from cars to laptops.
I'm too old to get away with "art student" anymore; these days I tell people I'm a civil servant*, which is not that far from the truth.
* Pro tip: choose or make up an obscure department that no-one ever has any business with. Statistics or internal auditing is good.