Just like what Awkward couch said, you need to block out the name, or Riot takes it as starting a witch-hunt. You can report it by going through the support link above (on the top bar).
You copy pasta, let riot know what happened, and hope they do something. You'll get a generic response like this after they reply to you:
We will investigate your report and take any actions we feel are necessary. Please keep in mind; we cannot disclose any disciplinary actions that may be taken due to privacy reasons.
Even if you were unable to use the report feature, please continue to use our in-game reporting system whenever you can. Reports you make provide us with valuable tracking information and help to escalate players to our attention for investigation. Each report brings violators of the Summoner's Code one step closer to restricted chat or suspension by our investigative audits.
Thank you for your patience and for taking time out of your day to send us this report. It is our goal to continue working towards making experiences on the Fields of Justice fair and fun for all Summoners!
Please let me know if you have any additional feedback or concerns.
So don't expect to hear if they do something. But afterwards just block the jerkwad and move on with your life. He ain't worth it hun.