It always starts with "Do you guys really believe this stuff"? How many threads like that are there on these forums? That's innocuous enough, but then they can't take the answer. "What?" "Your kidding!"
At this point many folks fall by the wayside, content to just lurk or look elsewhere for their fix.
But the true anti-believer goes a step further, because an innate need has awakened, a compulsion to convert the heathen, to educate the savages, to eradicate the heretics!. And so the symptom of Compulsive Round Earth Syndrome (CoRES) present themselves. These are twofold:
1. An increasingly and obsessive aggressive attitude towards anyone espousing the FE view. Any such most must immediately be refuted.
2. An insistence on the round earth, whether or not based on science. The latter case is especially funny because it tends to be of the "but EVERYBODY knows..." type.
Any other notable symptoms?