Expressions like "it is kind of you", "it is nice of you" are used to say that someone's action shows a particular quality. So If I do something nice to you, you say "it is nice of you". Similarly, if I do something funny/terrible, you might say "it is funny/terrible of you". I feel that "it is nice/kind/terrible/funny" should be followed by "to do that/this" or "to say that/this".
In "My nostrils flare" you do not do anything. Your nostrils do (flare). That's way "it is funny of you" does not quite work here. It does work when you perform a(n) (funny) action.