Apparently if you buy the "Brass Knuckles" from the shop, they get stuck to your hands forever since they do not count as a separate weapon.
This blocks your progression in an Achievement "Where's the Beef" that requires bare hand punching, and knuckles are considered a weapon (that you can't remove for some weird reason). Great work Ubisoft...
This needs the option to equip/unequip them ASAP.
Add Knuckles
https://www.youtube.com/watch?v=iuiZSxtodFM
&Knuckles
Sorry, couldn't help myself