A guy asks his drinkin' buddy if he had any suggestions on how to spice up a dull marriage. His buddy tells him "Well, you can always have an affair."
"I can't possibly do that! I would never cheat on her." he replies. So his buddy tells him "Look, if you convince her to let you do it, it won't be cheating." The guy thinks sure, that could work. And so he heads home, and finding his wife in the perfect mood, he springs the idea on her that maybe a new partner would add some excitement.
"Honey," his wife says, "that won't help our marriage. Believe me, I already tried it."