when it comes to; concerning ~
Expresses strong negative feelings or exasperation about a person or thing when bringing them up as a topic.
ときたら is used when you want to complain or show irritation about someone or something. It sets up the topic and then follows with a critical or exasperated comment. It often appears in spoken Japanese, especially in informal or conversational settings, though it can also be used in writing for effect. The nuance is usually negative: you are not just mentioning the topic, you are venting about it. For example, if a colleague is always late, you might say 'あの同僚ときたら、いつも遅れてくる' to express your frustration. It is not used for neutral or positive topics. You cannot use it to simply say 'as for' in a neutral sense.