"What's the wifi password?"
"121i362"
"It's not working."
"What wifi are you trying to connect to?"
"The United Airline."
"We're in the World Trade Center, though."
United Airline Wifi
Explanation
Explain Bear
Listen up, buttercup. This joke is dark. Someone wants to connect to United Airline's wifi but they are at the World Trade Center. You should know that the World Trade Center was attacked on September 11th, 2001. Two planes crashed into the Twin Towers killing nearly 3,000 people. It's funny because it's sad. Get it?
Jagged Zonkey
My guess is there would've been relatively little wi-fi on air way back in 2001, a quarter-century ago. If you were at an Apple AirPort, sure, but on an individual plane? "Airplane mode" was more likely intended to turn all the radios off so they didn't interfere.