Very low blows.
But nothing that justified your little puritanical outburst earlier.
So when would the word slut apply to a person?
Well, that depends on how you understand the word "slut."
For example, I would take it to mean a free, independent girl who does what she likes and looks great while she does it.
Other people might think that a "slut" is something akin to a prostitute.
I'm guessing you meant it in the latter, derogratry term, in which case it should apply when uh, you see a girl who is something akin to a prostitute?
... Nigel clearly isn't.
Although, if you meant it in the first fashion, then you probably could attribute it to Nigel.
Of course, I don't know you IRL, so I can't really say, but just for the point of this post.
Nigel, I do apologise if anything I just said offended you.