OK I found the logic, I just need to give different levels/permissions to "organizations" (for example a level called  "standard organization) and "persons" (keep the default level "standard"), where the organizations cannot befriend and persons can.

AND 

update menu's item visibility for the newly created level (for example allow the new level to see "add content" or "notifications" in the "Toolbar member") 

Bravo UNA :-)