Exclude single post from query post

How would exclude 1 post using the post id (321) in this code?

<?php query_posts("category_name=event-catering&showposts=100");
	if ( have_posts() ) : while ( have_posts() ) : the_post();
?>

I’ve tried adding &p=-321 like this:

<?php query_posts("category_name=event-catering&showposts=100&p=-321");
	if ( have_posts() ) : while ( have_posts() ) : the_post();
?>

.. but instead of excluding post id 321, it shows ONLY that post and excludes everything in the “event-catering” category..?

Thoughts?!