I report them for verbal harassment.

Honestly? Encourage them to report you and stfu. If they continue to spam you, report them for verbal harassment and /ignore them.

They typically leave you alone after they get the "talk to the hand" response from the GMs themselves.

GMs are very sympathetic, I have found. Just remember to tell them the name of the char, and the approximate server time that they pst/say/yell/General Chat spammed you those painfully slanderous and hurtful things.