From 9pm on April 25th, to 9pm on April the 26th everyone is obligated to send nudes on request. No questions asked.
Guy: "Hey, send you your tits"
Girl: "No way!"
Guy: "But it's national send nudes day!"
Girl: "Fine, but only if you show me your cock."
Guy: "Deal."
April 25th is national send nudes to a groupchat day, where everyone must sext a groupchat
Bob: What day is it?
Emily: National send nudes to a groupchat day!
Bob: Ok, heres a picture of my dick.
Emily: Ok, here are my tits.