To report a post, there's a little triangle at the top right of the post. Click that and it'll ask you for a reason for the report. You need to put something in there and then submit.
It's the second XXX I've seen this week. I tried to report this one ~ don't know if it got sent though because right after I hit submit, my internet connection died. But when i went back to try the report again, it told me I had to wait 60 seconds before I could report another post.