Scenario:
Client wanted to hide the ribbon from everyone except admin.
Solution:
Open your SharePoint master page
Add the following style in head section
style type="text/css">
#s4-ribbonrow { display : none; }
</style>
Now find the start of the "s4-ribbonrow" tag
and add following this:
<Sharepoint:SPSecurityTrimmedControl ID="SPSecurityTrimmedControl2" runat="server" PermissionsString="AddAndCustomizePages">
<style type="text/css">
#s4-ribbonrow { display : block; }
</script>
</Sharepoint:SPSecurityTrimmedControl>
Save the new master page and publish it.