How can I Expose Someone?

Who talks incessantly about themselves in the third person and attacks/slanders/hares other posters? This site is centered around this guy and who he dates. Various people post there, and they have called him on his bizarre behavior. Some of the things he says about himself aren't true (it's mostly boasting) and the poor girl he's dating has no idea, or she does, and just refuses to see it. He's using her for her means an it seems like everyone realizes it except for her. How is he able to get off with ostrasizing posters? Is there anyway to LEGALLY expose his behavior? I say "legally" because I would like to expose it without slander/harment, etc. on my end.