A condition in which a male best friend of a girl is in love with said girl, but is constantly shot down or ignored in favor of other men. When he does finally get a chance to admit his feelings, he is most often rejected in favor of being 'just friends' and will never get a chance to be with the girl again. There is no cure for Jacob Syndrome except to somehow find a girl you are even more in love with.
Joe: Olivia, I love you, and I always have.
Olivia: But Joe, I just want to be friends. Can't you understand?
Joe: Fucking Jacob Syndrome.
Olivia: But Joe, I just want to be friends. Can't you understand?
Joe: Fucking Jacob Syndrome.
by El Buzz Lightyear June 22, 2010
When you are an older male, yet your voice is almost like puberty is deciding and you barely have eyebrows. Please take a moment of silence for those with JSS.
by ZREX May 31, 2016