<?php
global $current_user;
$args = array(
'user_id' => $current_user->ID,
'post_id' = 100, // post ID. Can be '$post->ID' depending where you are calling this from
'count' => true
);
if(get_comments($args) >= 1){
echo 'disabled';
} else {
comment_form();
}
Function_Reference/get_comments
Based on AndrettiMilas code.