Just now, in the Low Quality queue, I came across an answer by a lovely lady who came to Stack Overflow to offer us all high-end escorts. I decided that "low quality" didn't quite seem to cover the problem, so after recommending deletion, I visited the question to flag that answer as spam.
Strangely, I couldn't. The flag dialog I got looked like this:
Why wasn't I able to use a spam flag in this case, and was I right to use an other flag instead?
(I think this is a link to the now-deleted answer, which I can't view: submitting a hyperlink by GET or POST)