Wordpress: Get the Deepest Terms. Supports Term order and Multiple Categories in Deepest hierarchy.

functions.php

<?php
function get_the_terms_deepest($taxonomies, $term_order = false) {
	$categories = get_the_terms(get_the_ID(), $taxonomies);														// get all product cats for the current post
	if($categories && !is_wp_error($categories)){																// wrapper to hide any errors from top level categories or products without category
		if(count($categories) == 1){																			// Case: Select only Category of Top Level. (Required: Activate Plugin Parent Category Toggler)
			$return = $categories;
		}elseif(count($categories) > 1){
			$return = array();
			foreach($categories as $category){																	// loop through each cat
				$children = get_categories(array('taxonomy' => $taxonomies, 'parent' => $category->term_id));	// get the children (if any) of the current cat
				if(count($children) == 0){
					array_push($return, $category);
				}
			}
			// term_order
			if($return && $term_order){
				$orderarray = array();
				foreach((array)$return as $value){
					$orderarray[$value->term_order] = $value;
				}
				if($term_order == "ASC"){
					ksort($orderarray);
				}elseif($term_order == "DESC"){
					krsort($orderarray);
				}
				$return = $orderarray;
			}
		}else{
			$return = false;
		}

		return $return;
	}
}
?>

index.php

<?php
$terms = get_the_terms_deepest("category", "ASC");	// The 2nd parameter is for 'term_order'. This is useful when multiple terms are returned. Available value: false or "ASC" or "DESC".
if($terms && !is_wp_error( $terms )){
	$termnames = array();
	foreach($terms as $term){
		array_push($termnames, $term->name);	// term_id / name / slug etc..
 	}
	echo implode(",", $termnames);
}
?>