You CAN NOT report enemy players
You can email Anet via their exploit email address with screenshots.
Reporting exploits:
If you discover an emergency game-breaking or economy-breaking bug, do not exploit it, but please notify us immediately at this email address: exploits (at) arena (dot) net. You may also use this email address to report suspected security vulnerabilities. Thank you to everyone who has sent reports. However, note that we cannot respond individually to emails to this address.