[chrishajer]

Or, the FAQ here:

https://bbpress.org/documentation/faq/#pretty-permalinks

Note, for people who cannot get this to work on a 1&1 server, you need to put this at the top of your .htaccess file:

Options -MultiViews

The Options +MultiViews does not work (IME) at 1&1, so in addition to creating the rewrite rules manually as in the FAQ, you need to DISABLE MultiViews to make this work. Worked for me.