Le Banquet D'Amelia was a movie playing in Sunnydale. In 1999, Buffy and Angel went to see the movie and were both surprised at what the movie was actually about. Buffy declared that it "Wasn’t what I expected. I’ve never actually seen... Well, from the title I thought it was about food." Both felt that they needed a cold shower after having seen it due to its "artistic" nature.
Very likely a reference to "Le Banquet D'Auteuil" due to the title similarity and the references to food being used in a sexual context.