Navigator > Setup > Company > Scripts > Script Events
Standard forms can be removed from the Navigator by removing permission for those forms.
However, you may want Users to have access to a data object, but not the corresponding Standard Form. If the user has permission, the standard forms can not be removed from the navigator, but you can use an OnOpen event to abort the form.
In the script linked to the OnOpen Event for the form, enter the following:
Abort("", True)
This will abort the form silently before it opens, meaning that although the form is listed in the Navigator, it cannot be opened.
You could add code to make this function applicable only to certain users or user groups. For example, to remove access to a form for a SALES user group, use the following code:
If User.UserGroup = "SALES" Then
Abort("", True)
End If