If you have a screenshot of something reportable but are unable to do so, you can submit a support ticket. That said though, anything from the game should be checked by the system. I would like to think that it checks post game chat, but I hear from time to time that it doesn't so I'm really not sure. Regardless, if you would like to submit one, do so.
For reporting, choose:
Request Type: "I have a question..."
Category: "Game and Features" > "General Questions"
You can add a description (tell them that it's for reportable behavior and whatnot) and attach your screenshot at the bottom of the page.