Someone or something you have heard a lot about. Not really a widely known person, but a friend of a friend or a local person (from your school/workplace/..). A thing you have discussed before, but is not well-known to outsiders.
Similar question: Looking for a word to describe someone who is famous to a small group of people
Cult hero from above question does NOT apply, and the best fit is the awkward and nondescript demicelebrity.
In my experience, people tend to colloquially use infamous with that sense (cf. The Infamous Swoosh) even though this does not match the dictionary definition.
infamous: well known for some bad quality or deed
I think peeps use infamous because they think of the word famous, but would feel silly using famous (the object in question has a more limited sort of "fame"). Familiar is close but not quite specific and expressive enough.
Contrived example:
I can't wait to meet your son Logan! I've heard so much (good stuff) about him! He's ________ [= well-known to me].
Actual examples from me texting:
> Me: https://68.media.tumblr.com/0dc47d322a9f8615dada2510ce522d20/tumblr_ojpmf5nYc41uy57v5o1_400.jpg
> Them: lol, I thought about the fast-food chains first, too!
> Me: i thought about Domains in the context of haskell
> Me: the infamous 'Dom' chain >_>
> [talking about modular smartphones]
> Me: that black guy from yesterday even has a video on them
> Me: next to techaltar's infamous video on them
What would be a better fit in this situation? Or am I stuck with demi-famous?