A joke can work through getting you to accept a false premise. If you have a pool boy, then you probably have pool.
Ronald Reagan brags to the Soviet about how free America is: A protester can stand at the White House with a sign saying Reagan is corrupt and senile. The Soviet leader responds: we have the same freedoms here: A protester can stand in front of the Kremlin with a sign saying Reagan is corrupt and senile.
There's a joke when a doctor prescribes an aphrodisiac. One sip right before sitting down to dinner and the couple goes at it, ripping each other's clothes off. The only problem... is that they are now banned from the restaurant for life.
Or the person who has been married 35 years, reflects on that on the death of their spouse. "I enjoyed 35 years of perfect happiness... and then I met my spouse."
Or the kangaroo joke some of my friends like. the kangaroo sits down at the bar, and orders a martini. Hands the bartender a 20, and gets a dollar back in change. When he is about to leave, the bartender says, "We don't get many kangaroos in here" and the reply is "Maybe you shouldn't charge $19 for a martini, then."

