Echo user category

I need the same thing. Please help. How to get current user group?

Please describe your request further.

<?php
    function replace_id_for_slug($option){
    	$categories = get_categories("hide_empty=0&taxonomy=product_tag");
    	preg_match('/value="(\d*)"/', $option[0], $matches);
    	$id = $matches[1];
    	$slug = "";
    	foreach($categories as $category){
    		if($category->cat_ID == $id){
    			$slug = $category->slug;
    		}
    	}
    	return preg_replace("/value=\"(\d*)\"/", "value=\"$slug\"", $option[0]);
    }

          $select = wp_dropdown_categories("taxonomy=product_tag&hierarchical=1&show_count=1&echo=0");

    $select = preg_replace("#<select([^>]*)>#", "<select$1 onchange='return this.form.submit()'>", $select);
    $select = preg_replace_callback("#<option[^>]*>[^<]*</option>#", "replace_id_for_slug", $select);
    $select = str_replace("cat","product_tag",$select);
    echo $select;
    ?>

I have an invoice template, and I would like to echo current user’s group name inside that template.
I tried this:

$terms = get_terms( 'user-group' );
echo ($user->user-group);

but, of course, it’s not working. It just echo 0.
How to do that?
Thanks