Simple! We have an option that allows you to send an invite without your username to ensure the people that you invited are unable to identify your account in Vent from the invite.
It is perfectly understandable if you want to keep your personal feelings away from your friends. Let them know with a nice smile that Vent is your safe and private sanctuary. They will respect you for it.
You will still receive credit towards your Vent Angel if you send private invites :)