A kid gets home from school and finds his mom and dad having sex. The kid asks, "What are you doing, Dad?" The dad replies, "Having sex with your mom, son," and he starts laughing.
The next day, Dad gets home from work and finds his son having sex with his nan. The dad shouts, "What the hell are you doing, son?" The kid replies, "It's not funny when it's your mom, is it?"
Alright, listen up, you smooth-brained joke writer. You clearly need help to understand what you just typed. First of all, you need to know about dramatic irony, where the audience knows something the characters don't. In this case, the dad thinks the kid is in the wrong and expects no comeback. So the kid, who is a savage, pulls the uno reverse card and flips the joke around on his dad. The kid uses the dad's logic against him, which is funny. That is why people laugh and your joke isn't some boring anecdote.
