MEGADETH So Far, So Good... So What! vintage backpatch
It comes from an 80s private collection. Some users on the site say this version could be original (see notably: http://tshirtslayer.com/patch/megadeth-back-patch-so-far-so-good-so-what) - it would probably date to 1988 or 1989 then.
It's been used, it's slightly wrinkled, but is still in a very good condition, as per pictures.