CBS

Season 5: Episode 22 - The Stag Convergence

The Stag Convergence: Leonard, Sheldon, and Koothrappali throw a classy bachelor party for Wolowitz, and Koothrappali accidentally lets slip stories about Wolowitz' perverse sexual history. When Bernadette learns about this, she gets upset and threatens to call off the wedding, but Wolowitz gives a convincing and heartfelt apology that wins her over.