Dear Y-W-P, I bought I jacket last month that looked great on the [display] model. Now when I wear it it looks different. I wear a 38/40 jacket and I am slim. I know that I need to have it "taken in". How tight is too much to take in the middle?
If it looks good on the mannequin, it has a 50/50 shot of looking good on a human. The jackets and clothing are pinned and stretched endlessly on displays to look great. Since most male displays are tiny 34-38" chests and don't move, the jackets are tightly wrapped on them and look deceivingly good. The shoulders/waist ratio is also statistically uncommon.
This is a bit too tight in the middle.
No tailoring magic... just pins and folds.
As for taking in jackets, the torso-tightness is purely the preference of the wearer. I like them slimmed in the middle, but loose enough that a thinner wool sweater can go underneath. As a general guide, I would say that lateral creases or puckers mean that it is too tight. Even if you are unfamiliar with tapering them, a few minutes with a seamster or tailor will bring you to a comfortable level. It's fine to be a little picky with the pins and insisting "A little more... a little more" is perfectly reasonable for fitting garments. What never ceases to surprise me is how minuscule differences can make a difference... quarters of inches sometimes. Sleeve length, lapel width, and all angles of the clothing drastically change the overall look.
This is not to say that you should obsess about quarters of inches. You should merely adjust the jacket to a point that you think looks good. Remember that it should also be comfortable and look good not just while standing at the fitter's mirror, but most importantly, while moving around living your life.
P.S. I'll be in that fine city of yours next month.