He FAF bro. that's how.
Symptoms may include
1. Obsession over said Anime.
2. Continuance of Poorly (or well done) fan art of said Anime
3. Cosplay of cast from said Anime.
4. Annoyance of anyone within 10 feet of the infected individual.
If cured from FAFS the victim may suffer from
1. Loss of friends.
2. Loss or gain of weight.
3. Loss of Charisma.
4. Unfunctioning member of society.
Anime that may spread FAFS
2. Full Metal Alchemist
2. I heared when Sally saw Inu-Yasha, she was rejected from her closest friends because they wanted to stay clear of FAFS.
3. "Remember kids. Don't date people with FAFS."