Disclaimer; If I owned The Avengers, I'd be in the Bahamas with Tony Stark.
It was the 21st of December, 2012. The day the world was supposed to end. So they (Tony) decided that if they were going out, they were going out soused. Bruce started talking about Mayan cultural history and they collectively worked out that they could save the world if they sacrificed a virgin on the landing-pad of Avengers Tower.
Steve had to run for his life.
