You can report the user by pressing and holding the message you want to report, and then tapping Report.
When you report a user, the message being reported, and messages appearing before and after that message (up to nine) will be sent to the REALITY Operations Team.
All reports are reviewed by the REALITY Operations Team.
The situation will be investigated, and if determined to be against our terms of service, appropriate actions will be taken.
You can also block the user to prevent receiving further messages.
From the message screen tap Settings > User Details > Block to block the user.