Have you ever fooled around with another man in front of your husband/boyfriend with his encouragement?

This is a question for the more adventurous, not the Christians amongst us!
 
My man has revealed his fantasy of watching me with someone else. Apparently it's all about my getting maximum pleasure.
 
It's not that uncommon a fantasy really. For us, it's only talk for now.
 
I'm curious to hear from anyone who has tried it, or something similar.