Mine works fine without the trailing /. Here is part of mine:
RewriteCond %{HTTP_REFERER} !^
http://smutbandit.com.*$ [NC]
RewriteCond %{HTTP_REFERER} !^
http://www.smutbandit.com.*$ [NC]
and my rewrite condition is different:
RewriteRule .*[Jj][Pp][Gg]$|.*[Gg][Ii][Ff]$
http://smutbandit.com/errors/