<?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.