Yeah, I saw when bobc mentioned the button for reporting posts. Most forums have one, and I thought it was missing here; at first I thought it was the little blue button to the right of "Quote" but that's not it. When bobc mentioned it I looked harder and started clicking things and found it.
It's badly placed and not obvious. It looks like it has something to do with contacting the user...
Anyway, just to be perfectly clear, it's this button: