In the comments.php file of your theme, find this code:
<h2 id="comments"><?php comments_number(__('No Comments'), __('1 Comment'), __('% Comments')); ?>
<?php if ( comments_open() ) : ?>
<a href="#postcomment" title="<?php _e("Leave a comment"); ?>">»</a>
<?php endif; ?>
</h2>
See where it says ("Leave a comment") .. go for it! On my husband’s blog (he’s a former cab driver), it says Shout at the driver!. 🙂
And you can also change the text above, ('No Comments'), ('1 Comment') and ('% Comments') to whatever you want if you like. For example, on my husband’s blog, I’ve got All’s Quiet in the Backseat, One Backseat Driver and % Backseat Drivers, respectively.