I've always hesitated to use 4 ply yarn to knit an adult-sized garment that's not for me (it would be a bit of a heartbreaker if it was rejected, for all the time put in); that is, until now.
This is H. He is 12, and will be taller than me in a blink of the eye. I can just squeeze into the vest, so when all three boys outgrow this, it will be mine! :-)
The pattern is from Martin Storey's Classic Knits for Men (UK version, it's the vest on the cover) or Knitting for Him (US version). The yarns used were Rowan Yorkshire Tweed 4 ply (7 balls Stainless, and 2 balls Explode), and Rowan Scottish Tweed 4 ply (a softer, more fragile cousin, 1 ball each of Lobster, Mallard, and Apple). These are pretty much the same colors as the original, except with a brighter red and dark green (so bold of me to change colors like that, heh). The only mods I made was to knit it slightly narrower, cast on with 10 fewer stitches in the back and 5 fewer stitches on each front than the smallest size, and lengthened the armhole a tad, because the pattern has a 7.5 inch armhole, which would be small, even for me.
One thing that irks me about this pattern is that there are no pictures that show the tiniest bit of the back, so it was a surprise upon reading the pattern, that there's no fairisling in the back, just all textured rib. It turns out I quite like the contrast of the front and back.

There's very little seaming to do. After three-needle binding off the shoulder seams, there was only the band at the back of the neck, and the side seams to do, thanks to the intarsia bands that are knit at the same time with the rest of the body. There were some tangles along the way, but I still preferred that to seaming!
Not only is there less seaming, the decreases along the fronts and armholes look neater too.

The all important buttons...
These pictures were taken after a few wears. (H may be too embarrassed to hold my hand in public, but he hasn't scorned the handknits yet, and he's worn this vest without any prodding.) It's holding up remarkably well, probably in part due to the dense fabric created by a gauge of 10 rows per inch.
Another gratuitous innards picture (the colors look most accurate here). Just bear with me; I like this knit a lot! ;-)