Beethoven was premiering his piano duet, March (op. 45) with duet partner Ferdinand Ries. When a young count spoke loudly to a lady friend in the room next door, Beethoven jumped up and shouted “I will not play for such swine.”
Source: Arganbright, Nancy (2007) “The Piano Duet: A medium for Today”, The American Music Music Teacher, Vol. 56, issue 5, p. 16.