Back when the wife and I played together we arranged a role-play where the wife would come home from work and would bust me with the lady. Then I'd be "punished" by being their boy-toy slave and service them as I was told.
We had known this lady for three years and she knew the plan. Wifey was all excited. Hel I'd get to bang two women so "duh" on my excitement.
Still. The lady and I were laying there buck assed naked fully knowing the wife was about to walk in on us and we both STILL jumped up and started scrambling when we heard that door open. Must an "Oh shit I'm busted" automatic reaction in us.