Tailor wanted to put darts in my dress shirt, but it is already darted.

Might start looking like a woman's shirt in the back with multiple darts.

It's easier to add darts than open the shirt seams at the sides and narrow the shirt.
You might want to ask another tailor.

This:

 

 

Another option, darts in the front and the back. But that's usually a style reserved for sleazy italian or greek waiters at restaurants.

 

Double darts in the back look strange to me.

Perhaps try a different make requiring less alteration would lead to a happier outcome?

multiple darts at the back would look too weird, and it would depend on the fabric material.

You can have 'four' darts on the back without being able to see any more than two seams from the outside. I've had this done to shirts before.

Well I've never seen 4 darts yet on a shirt.

He may just make the original darts deeper

^^^ that's what I was thinking. On a side note high street fashion brands to the masses seem to have gone insane with darts now. Not only you get the usual back dart and the vertical front darts that you really should only see on womens wear now I see stupid darts starting from underarm angling inwards to just under the nipples.

Agree. Also, you don't need to rip the original side seams to take shirt in from the sides.

Yo dawg, I heard you liked darted shirts, so we put darts in your darts, so that you can wear darted darted shirts with darts.

My tailor will not put darts

I do my shirts without darts. Don't like the look of em.