It seems to become increasingly difficult to get the built-in apache on our Macs to play nicely with virtualhosts...
Following the standard procedure from a numberof forums and support pages, I changed on "AllowOverride None" to "AllowOverride All" in my /etc/apache2/users/USERNAME.conf file, and all of my sites started to be forbidden.
I changed it back and and then changed it only for one site in my httpd-vhosts.conf file, and only that site was forbidden.
After looking at the logs and seeing the problem was with url rewriting and the lack of FollowSymLinks, I went back to the USERNAME.conf file. I switch "AllowOverride None" to "AllowOverride All" and added "Options +FollowSymLinks" on the next line.
Things started working. I came from using xampp on windows and it had a lot of these settings already set server-wide for dummies like me.