He goes to the doctor and says, "Look, I just can't bring my wife to orgasm in bed, it's a real problem."
The doctor says, "Well, is it too warm?"
"Yes, it's absolutely sweltering"
"Then get some air-con"
"I can't afford air-con, I'm too poor"
"Well, Dave, do you have a good mate?"
"Yeah, I've got a mate Francis"
"Well, ask your mate Francis to stand over you and the mrs with a towel, wafting you both to cool you down, that might help."
So, Dave asks Francis for this favor, who then agrees to help him. That night, Dave is in bed with his wife, pounding away with Francis fanning them with the towel but it's doing nothing for her.
Dave says, "Well this isn't working, let's swap." So Dave takes the towel and starts wafting Francis, who is now shagging Dave's wife.
Not long after, Dave's wife goes "Oooh... oh that's it, I'm about to cum, I'm going to cum!"
Dave shouts, triumphantly, "You see, Francis?! That's how you waft a fucking towel!"