Normal players can use and abuse @a, @p and @r selectors in /tell and /me. This allows them to pinpoint other players by adding arguments to the selectors, like: /tell @a[name=Person_I_Want_Dead, x=100, y=100, r=1000]. This message will only send when those requirements are met.

This also works in /me, which allows players to spam the chat with /me @a @a @a @a @a @a, potentially crashing servers.

A suggested solution is to only allow selectors to be used by OPs and command blocks.