No knock knock joke, but still a good one:
A woman went to the doctor trying to find a way to make her husband stop farting in bed. The farts had so much force, they would knock him out of the bed. She told the doctor that it happened at around 4:00 every morning. The doctor told her of a remedy that might scare him into stopping, and she figured it was worth a shot. He told her to get some chicken meat and put in in his drawers before he started, and maybe it might give him a little scare.
She got up the next morning at 3:45 and quietly shoved the meat in his boxers, the trap was set. She thought she might wake him up by laughing, so she decided to go down and get some coffee. At exactly 4:00, she heard her husband let one loose. Seconds later she heard screaming. She took another sip of coffee and waited for her husband. A few minutes later, the man came down and said to her:
"Honey, I think I just shit out my intestines. But with the help of God and a curtain rod, I got 'em back in there."
Typed from memory, so sorry if it's jumbled up.