Open Graph Description + Mentions?

There really isn't. While there is a way to 'tag' friends when an Open Graph Action is taken. However, 'mention tagging' can only be used for users that are doing something 'together'. The examples are checking into a restaurant together.

developers.facebook.com/docs/opengraph/guides/tagging/

Ultimately, we don't currently have the ability to support the tagging you mention. However, if you feel that what you want to do is something that would be inline with Facebook's description, let us know. We may be able to help you implement it. It won't be immediate, and again, you really would need to be sure it would work with Facebook's guidelines because there's an extra approval process required for user tagging in actions.

I hope that helps explain, and let us know your thoughts.

Thanks,
Alex

No problem for clarifying. If you have any other questions, don't hesitate to let us know. It's confusing what's possible, and what isn't.. and that's why we're here.

Thanks,
Alex