I've had this tshirt refashion on my Upcycling Pinterest board for a while. Then a few weeks ago I ran in a 5K and finally got the perfect shirt to try it out.
All they had left were larges, XLs and XXLs when I got to sign in. I had pre-registered for an XL, but I felt bad that all of these skinny runners were getting stuck with huge shirts, so I voluntarily took the XXL size instead. It is pretty roomy!!
Cut off the arms and the top/neck portion.
Turn the shirt inside out. On the top of front and back, fold down about an inch and a quarter to sew a ditch for running your straps through.
Cut off the reinforced band of the sleeves and use those as straps. Run them through the channel you sewed, then sew them together in one large circle. (Then I shifted the circle so that that sewed part was hidden.
Voila! The armpits are a little low for my taste, but I think that is because the shirt started out too big for me. But still...it looks really cute over a ribbed-under tank and some black running capris. :)