To ping a user in a post, you usually just type @ directly followed by their user name.
This sometimes fails if the user has special characters in their name.
For example, to ping @Peter Mosevich that has a space in his user name (how are you buddy ? any new pico-8 cart or puzzlescript in preparation ?), you can use @ then { then the user name with the space, then }.
This has worked for me so far, but today, I tried to ping a user (cat-8) that has a minus sign in his user name, and I ended up pinging user cat instead (sorry).
Does anyone know how to properly ping such a user ?

I don't know if this is the solution, but perhaps try backwards slash () before the special character.

@AntArrow , nice try but no.