SINCE WHEN

Huzaifa AsifLike, is it okay to say "Since when you have become so boring?"
or "Since when you have been working in this company?"

No.

When did you become so boring?
Since when have you been so boring?
Since when have you been working in this company?

So we use perfect tense while using 'since when' most of the time?

Yes.

Since when is $250 too expensive for a nice watch?
Or
Since when has $250 been too expensive for a nice watch?

The former sentence is correct.

Huzaifa AsifSince when is $250 too expensive for a nice watch?
Or
Since when has $250 been too expensive for a nice watch?

Hmm. I take back that yes. Although since is usually used with the perfect tenses, questions beginning with since when are often idiomatically used with the simple present. Your first sentence, Since when is

Questions beginning with since when are often used with simple present? but there's a sentence in your post in which you have used perfect tense despite the fact that it's starting with since when& it's a question.

Please clarify.

Please read this one: http://www.EnglishForward.com/English/SinceSinceYou/brjbkv/post.htm.

Huzaifa AsifQuestions beginning with since when are often used with simple present? but there's a sentence in your post in which you have used perfect tense despite the fact that it's starting with since when& it's a question.

Sorry for the confusion! Your third post reminded me that the simple present is actually very commonly used in since when questi

Oh thanks for a detailed answer.

Is it fine to say "Since when you are working in this company?" than "Since when you have been working in this company?"
and the difference between two? The latter one indicates that listener expects you to tell you how long he is been working in that company and the former one?