Add taxonomy slugs to post class

gistfile1.php

<?php
/**
 * Add taxonomy slugs to post class
 *
 * @author Jared Atchison
 * @link http://jaredatchison.com/code/
 * @param array $classes
 * @global array $post
 * @return array
 */
function ja_portfolio_post_class( $classes ){

	global $post;

	$custom_terms = get_the_terms( $post->ID, 'portfolio-features') ;

	if ( $custom_terms ) {
		foreach ( $custom_terms as $custom_term ) {
			$classes[] = 'tax-' . $custom_term->slug;
		}
	}

	return $classes;
}
add_filter( 'post_class', 'ja_portfolio_post_class' );