It's a very common complaint around here ...
Well, here's a fix for that if it's not too badly stretched out yet or too oversized to begin with. This thrift store find of Curiosity was still in good condition to be a candidate, and I'd hate to see a @fishbiscuit shirt go to waste, as unsold shirts usually end up going to rag houses where they're cut up and turned into rags.
DISCLAIMER: PROCEED AT YOUR OWN RISK. I'm not responsible for damaged shirts, sewing-related injuries, etc.!
A properly fitting shirt for comparison. I'm using Youbetchücan! today.
Scissors with a pointy tip or a seam ripper.
3/8" wide elastic band.
A safety pin.
Color matched thread and needle.
Deconstruct the seam at the neck hole ribbing. You will only want to do the inside of it.
Cut enough elastic to go around. You will rather err on the "too long" side right now, as it will be re-cut after adjusting later.
Pin the safety pin on one end, about a quarter inch from the end.
Thread the elastic through. Use your fingers to push, pull, push, pull ...
Completed, but maybe a bit too small!
No worries. Re-pin the two ends together (so the elastic doesn't inadvertantly pull back inside) and work your way around the neck hole, adjusting the opening. Compare it against your properly fitting shirt. You don't want it to be too tight as to pucker the fabric, but you don't want it so loose that it doesn't help to keep the neck hole's shape (which is the whole intention here).
Adjusted now, make sure the elastic sits flat. Unpin them, cut off the excess leaving a small overlap so you can sew them together flat.
When done, sew the seam shut.
From the outside, it'll look no different.
Compare it to your other shirt ...
... and how it looks on its own.
You can see some slight ripples, as it's tighter than "normal", but otherwise, this will be about as close as one can do to make them "wearable" until we get something better. There's not much that could be done about the excessive shrinkage, though. As for the width of the women's shirts, Ochopika posted some re-sizing instructions here. Again, proceed at your own risk.