Garry's Mod is being messed with by a hacker who's manipulating Lua code to send a virus that changes people's names and make them spam "VINH'LL FIX IT" or "FIX IT VINH."
The virus is being transmitted through infected servers that contain !!! or # in the name. Avoid these servers in particular, and if an individual with a name akin to the phrases above joins your server, leave immediately. The virus is most likely harmless, but manipulation to the code (a prominent add-on developer was implicated in the code a few hours after the virus' spread) may lead to a change in potency.
I would avoid Gmod entirely until the issue is resolved.
EDIT: The issue has been resolved. Gmod's been updated, and the exploit has been fixed, but it is recommended that you uninstall and reinstall the game entirely before playing online.