What it means
ときたら attaches to a noun and singles it out as a topic, usually with exasperation, criticism, or strong disapproval. It means “when it comes to” or “as for,” but unlike a neutral topic marker, it commonly implies that the speaker is about to mention a particularly troublesome or remarkable quality. The clause that follows is normally negative, critical, or otherwise emotionally marked.
Usage note
ときたら is not a neutral replacement for は or について. It is most natural when the speaker has an evaluative or emotional comment about the topic, and it is generally more conversational than formal written language.
How to use it
弟ときたら、約束の時間を毎回忘れます。
When it comes to my younger brother, he forgets the agreed-upon time every time.
弟ときたら、約束の時間を毎回忘れる。
When it comes to my younger brother, he forgets the agreed-upon time every time.
Example sentences
うちの弟ときたら、試験前日になってもゲームばかりしている。
When it comes to my younger brother, he does nothing but play games even on the day before an exam.
新しい市長ときたら、公約を一つも実行しない。
When it comes to the new mayor, he does not carry out even a single campaign promise.
あの食堂ときたら、昼休みになるといつも長い行列ができる。
When it comes to that cafeteria, a long line always forms as soon as lunch break begins.
山田