Question: I'm normally pretty good with grammar, but this one just stumped me. I was trying to write something similar to "you're one of the only people who [is/are] nice to me", but I'm not sure if I should use "is" or "are".

Which sentence is correct, and why?

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> You're one of the only people who is nice to me.
> 
> 
> You're one of the only people who are nice to me.
> 
> 
>

Answer: 
Correct Sentence is **You're one of the only people who are nice to me.** 

That is because in this sentence we check agreement of the *verb* **are** with the *plural noun* **people**. 

Here the [verb depends on agreement with the noun](https://webapps.towson.edu/ows/sub-verb.htm) i.e Plural Noun - Plural Verb or Singular Noun - Singular Verb
The sentence makes no sense as it stands. Perhaps you mean something like this?

You're one of few people who are nice to me.

You're one of only a few people who are nice to me.

It's not clear what you mean, but at least your words "one of ... people" shows that you are speaking of the other person as one of some plural group of people who are nice. As Mohsin Kamal says, this means that the verb should be "are". But "only" makes no sense. Only what? "Only a few", perhaps? "Only" and then some number, perhaps?