If I said “she comes off as intelligent”, doesn’t that mean “she appears smart”? (Same as “comes across as”).
I always thought that was a valid phrasing, but the dictionary doesn’t list anything remotely close; it just says “come off” = “happens or succeeds at”.
Have I been using a nonexistent idiom my whole life?
That question comes off as confused. 
From Merriam-webster dictionary.
Ah. Maybe it just wasn’t the right dictionary. First time Dictionary.com’s actually failed me… good to know 
It is an idiom, but a slangy one; much more so than “come off” =“succeed” (of a plan, scheme, project etc.).
Slang, huh? It’s not a regionalism, is it? (Cali here)
I always felt that “comes off as” has a vague derogatory connotation.
As in, for example, “she comes off as intelligent” contains a slight whiff of “she comes off as intelligent (and as being bit snobbish or stuck-up about it)”.
It’s very commonly used in the UK, if that helps.
No, only if that is the intent of the person using it. Generally it just means seems or appears. Here are a few quick quotes:
Ironically, this adolescent comes off as the strongest person morally in the picture…
Paul Nitze, the negotiator for intermediate-range forces, comes off as heroic, if tragic.
An articulate and intelligent man with a subtle sense of humor, in person Cetrulo comes off as more an Ordinary Joe than Maximum Bob.
*
Loeb never comes off as angry — just really hurt and, like, a little sad? *
*America comes off as a heartless, chromeplated, centrally heated jungle in which people lose all of their simple, rural virtues. Ireland, despite Tom Maher, comes off as a little bit of heaven that fell from out the sky one day. *
Around here (Saskatchewan and New Brunswick), it’s often used as a set up to deny whatever was set up, as in “she comes off as intelligent, but she’s really just read a book or two and quotes their arguments.”
I agree it has a slight negative connotation. But it’s the way it’s used. If you say “She comes off as intelligent” it’s not the same as “She is intelligent”. It implies you can’t tell the book by it’s cover.
Interesting relationship to a more literal meaning, removeable. Will that paint come off? It’s as if it’s describing a veneer when it’s used in the sense being discussed here.
I also think it CAN be used to imply a negative or the opposite. Not that is always or even mostly is used that way.
“He comes off as pretty stupid.”
IMO when somebody says something along those lines they usually mean he only “comes off” as stupid, not that his actually is.
To me “she comes off as intelligent” implies that she seems intelligent, but isn’t really. Sort of a back-handed compliment.
“With his winning smile and egregious personality, he comes off as friendly (but he’ll stab you in the back first chance he gets).”
“This investment strategy comes off as a big come on.”
My read of the connotational meaning of “come off” is that it implies the idea of a mismatch between intention and results. “He comes off as a jerk (although he doesn’t realize it)” or “She comes off as smart (although she really isn’t)”.
Maybe that’s just in the typical construction and context of statements using “come off”, just because they emphasize appearances. “He’s a jerk” makes a statement about actuality (at least from the perspective of the speaker); “He comes off as a jerk” makes a statement about appearances. Someone who makes this distinction is either intentionally honest about the limitations of perception (“He appears to be a jerk, but I don’t know what he’s really like”) or else trying to draw attention to a dichotomy between appearance and reality (“He appears to be a jerk, but inside he’s actually the biggest sweetest teddy bear you could ever meet.”)
I don’t think it’s necessarily derogatory either. By describing appearances only, it intentionally leaves room for a different conclusion, but I don’t think the different conclusion is necessarily implied.
I only use the expression in my life when I don’t have enough knowledge about someone to know whether I’m saying something true or not - so I use it a lot when discussing job candidates after the interview. I don’t want to say “She is intelligent” when I met her 10 minutes ago. So I might say “She comes off as intelligent” to qualify that I’m just reporting a first impression.
Two different idioms are in play here, thus the confusion:
Come off = happens
Come off as… = happens like…
Because of the ‘as’ in the second phrase, it sets up the opposite meaning because ‘as’ can be used to mean similar, but not necessarily the same, and therefore, completely different in reality.