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.
If you're 'festered', you're stoned to the bone, maybe you're drunk as a skunk, or perhaps both. Either way, you're an inebriated son of a bitch with the munchies and a 'let's fuckin party' kinda attitude. Popularly used in Santa Cruz, California.
Dylan was so festered last night, he chased his tequila with a bite of mac n cheese.