Remove menu items (hide menu items) for everyone except a specific user.

functions.php

/*
* See http://wordpress.stackexchange.com/a/28784/16 for all options
*/
add_action( 'admin_menu', 'my_remove_menu_pages', 9999 );
function my_remove_menu_pages() {
    global $current_user;
    $username = $current_user->user_login;

  if ($username !== 'SPECIFIC-ADMIN-USERNAME-HERE') { 
        remove_menu_page('edit-comments.php');
        remove_menu_page('edit.php?post_type=acf');
        remove_menu_page('plugins.php');       
    }
    
}