David Letterman and Drew Barrymore discuss how her flashing him on his birthday in 1995 impacted both of their lives

Letterman surprised Barrymore on Monday's The Drew Barrymore Show for her 46th birthday, 21 years after she famously went on top of his desk and flashed him for his 48th birthday in 1995. Barrymore credited the moment with making her realize the value in being spontaneous. "I recognized it immediately as being unique," added Letterman. "It not happened prior to me. It's not happened since to me. And later I was thinking, 'oh geez, what if she does on Leno's show?' Then I'll really be upset. But it was kind of a connection for us throughout the rest of our existence here." Barrymore responded: "I felt you compelled me in a moment to take a risk, and you allowed it to be paid off with kindness and reciprocity and goodness and humor, which is ...honestly, I think that is the greatest award and reward that people could give each other."