In the rich text editor:
@Floofiedog
In a comment:
[Floofiedog](https://chowlings.com/user/Floofiedog)
For Names and Avatars:
In the rich text editor:
%Floofiedog
In a comment:
[![Floofiedog's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/Floofiedog) [Floofiedog](https://chowlings.com/user/Floofiedog)