In a custom html field I added "[cb:if user="#displayedOrMe" user_id>"0"][username][/cb:if]" (togehter with more info, so I don't use the username field itself)

That IF condition will never fail. You're using #displayedOrMe and when it comes to a field the #displayed is always the profile owner. What are you trying to do exactly? Only show that if someone is logged in? If that's the case the below is what you'd use.

[cb:if user="#me" user_id>"0"][username][/cb:if]

ok, NOW I found the info, doesn't work, I am using the CB content module ...

That IF condition should work fine in CB Content Module, but it's still going to work as explained above if it's inside of a Custom HTML field being substituted into a CB Content Module. The #displayed part is checking for what user profile is being viewed and the OrMe part is checking the user viewing the page. So if you're viewing a profile it will display the username of the profile displayed otherwise it will show the username of the person logged in.

See the substitution tutorial below for further usage information.

www.joomlapolis.com/documentation/279-community-builder/tutorials/18353-using-substitutions-throughout-cb