A rejection that new photography students feel of the controversial theories about photography presented by Susan Sontag - in her 1971 book On Photography. It is a blend of "antagonism" and the mentioned cultural theorist and activist's last name. She's also known for having a relationship with Annie Leiborvitz, you know, the chick that photographed John Lennon with Yoko Ono.
Sontagonism usually results when people who just want to take photographs with their digital camera are assaulted by theories of Sontag at University or art school - much like how Sontag claims that taking photos is an assault in itself, likening it to a "gun-fantasy" where photos are "shot".
Greg's got some major Sontagonism, bro, his professor is gonna get it in the neck!