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