TKS is a demeaning and negative term that should be used in moderation. Sometimes the victim can overcome the syndrome, however once made aware of their mistakes, the syndrome can take over control and have disastrous effects.
TLDR: Too Keen Syndrome (TKS) is a term used to describe people with an extended/unnecessary interest in someone/something. Beep Beeep
Jim: "Haha so anyway I left hers and half an hour later I get a text asking what i'm doing tonight"
Jon: "She's definitely TKS mate"