Another member is being rude to me in a Conversation. Can I block them?

Absolutely. You can block another member from contacting you through a message by opening up the conversation you are having with them and clicking the red arrow in the top right corner of the message thread.

Choose "Block User" from the resulting dropdown to block the user from being able to contact you through Conversations. This will also prevent that user from commenting on any of your recipes or posting in groups you have started.