try {
    Context.openSession();
    Context.addProxyPrivilege(PrivilegeConstants.VIEW_PERSONS);
    UserService us = Context.getUserService();
    User user = us.getUserByUsername("tata");
    us.retireUser(u, "Not used anymore");
} catch (Exception e) {
    e.printStackTrace();
} finally {
    Context.removeProxyPrivilege(PrivilegeConstants.VIEW_PERSONS);
    Context.removeProxyPrivilege(PrivilegeConstants.EDIT_USERS);
    Context.closeSession();
}