Mod Rewrite apache help

Hi, I’m having some issues working out how to phrase a certain rule.

Basically I want certain folders to act as normal, as my main rule is pretty all encompassing.

RewriteEngine On

RewriteRule ^!((rss|assets|forum)/?)$ $2/ [L]

RewriteRule ^([a-z0-9-]+)/?([a-z0-9-]+)?/?([0-9+])?/?$ index.php?1=$1&2=$2&3=$3 [NC]

what I’m attempting with that first rule is that someone who goes to:

website.com/rss or website.com/rss/ (an actual directory btw)
ends up at website.com/rss/ (using L flag to make it the last rule)

I can’t seem to quite get why it wont apply :confused:
Am using this cheat sheet: http://www.ilovejackdaniels.com/cheat-sheets/mod_rewrite-cheat-sheet/