"The One With Monica's Thunder" is the seventh season premiere of Friends, which aired on NBC on October 12, 2000. Minutes after Chandler proposes to Monica, she plans to celebrate on the town with her friends - until she catches Ross and Rachel kissing.
It's still the night of Monica and Chandler's engagement and they all dress up to go drink champagne at the Plaza. Rachel is a little sad and lonely and asks Ross whether they want to have a "Bonus Night". Monica catches them kissing and is upset because she waited her whole life for that day and thought it would only be about her engagement but now it is about Rachel and Ross getting back together - they stole "Monica's thunder". Monica is really upset and doesn't want to go out for champagne anymore. Monica and Rachel have a huge fight and Rachel admits that she kissed Ross because she was sad about not even being close to getting married. Monica forgives Rachel.