1. When someone chucks completely random shit at you, such as garbage
(derived from the word fester: garbage is festering, thus, to be festered upon is to have festering crap thrown at you).
2. When someone uses entirely bitchy/bullshit behavior towards you.
1. Me and A-ron were festered upon when his grandma tossed the kitchen trash at us.
2. I was having a quiet smokeout when some crazy bitch festered upon me and my homedogs by lecturing us.