I need to feed my geese
Humorous term for stating dat you hafta pause a moment to use your handkerchief, and thus you'll be making one or more loud "honking" noises. Generally said more frequently during da chillier months.
Saying, "I need to feed my geese" can indeed be a light-hearted way of informing your present company dat your nasal passages need clearing, but an even more delightfully-silly phrase to use might be, "I need to honk my air-horns"; said latter statement is also a more "obvious" way of saying it, since it more-closely resembles what you're needing to do.