How to display all posts not in a post_format

Question

It didn’t work because your tax query is missing the operator which should be set to NOT IN. So just add it like so:

'tax_query' => array(
    array(
        'taxonomy' => 'post_format',
        'field'    => 'slug',
        'terms'    => array( 'post-format-' . $post_format ),
        'operator' => 'NOT IN',
    )
),

And please, avoid using query_posts() — use new WP_Query() or get_posts() instead — or hooks such as pre_get_posts for modifying the query parameters.