Guys, you shouldn't joke about 9/11.
My great-uncle died that day. Best damn pilot in Iraq.
Listen up, buttercup. The joke is playing on the tragedy of 9/11. The setup makes you think the person is going to share a sad story about losing a relative in the Twin Towers. But the punchline reveals the relative was a pilot in Iraq, implying they were a casualty of war, not the terrorist attack. It's funny 'cause it's unexpected and twisted. You probably thought Iraq was in Vietnam or something.