I hope the next line haunts you as much as the mental picture you have given me.Next time I have an MFM threesome with a guy with a really big dick, I'm gonna ask him if I can stand naked right behind him, reach around, and hold his dick for a second... see how it feels to have a huge one
(this really is a random thought and I hope it will never come back to mind)
Maybe the guy will ask to stand behind you and hold yours, just to see how it feels like to have an average one.