My greatest fantasy would be to have my wife bring home a man for us to share.  She would make me wear a pair of her panties.

After watching him fuck her, I would be be required to suck his cum from her just filled pussy.  My cock would be hard and throbbing in the little panties while I ate his cum from her.  She would get off and giggle at my arousal of eating another man's cum. 

Both the guy and my wife would be turned on watching me get hard in the panties eating his cum from her.  She would then be standing next to him and making out with him when she has me get on my knees in front of him. 

She would hold his cock for me and they would make out as she makes me suck him off.  She would giggle as his pumps my mouth full of his cum.  She then makes me jerk off in front of them and eat my own cum out of the panties.