How do I báo cáo someone? Please help! Details below.

I received a message from an idiot called Firefly6m.
First off he thought I was a guy which was stupid (hello, my username!) but he was asking for sex and to Google him if I was interested! I blocked him but I want to báo cáo him but I don't know how? How do I báo cáo someone on FF and can I even do that?

Please help!