I understand the desire for adults to have a shirt that fits, but I think that falls squarely in the bucket of "nice to have". As a parent of a child that doesn't fit any of the sizing charts, being able to predict what size of what brand will fit my kid would be a "must have"! Kids also tend to go through clothes a lot faster than adults, making the potential savings of getting a good fit far greater.
I organize an annual conference [1]. All of our attendees get a free tshirt. We purchase all of our tees from a single manufacturer (say American Apparel) and let the attendee tell us the size they want before we finalize the order.
The problem is that attendees often don't know what size will fit them, and sometimes guess wrong and end up with a poor fit. Anything you could offer us to help here?
PS. Could you include "stretch" t-shirts, like this one (just an example):
> http://www.iwantpants.com/polo-ralph-lauren-stretch-cotton-w...
http://www.dailymail.co.uk/femail/article-2459720/Tommy-Hilf...
I hate you.
.
(hey, you downvoters: that's a joke)