Funny, I'll put my feet (in socks) on the bulkhead but I won't do this as it is clearly against the boarding rules.
Assuming you're sitting with the companion, it's much better for everyone if you bring them on with you. It's way more efficient to seat two people sitting in adjacent seats together. No one else happens to get up and bags can generally be stowed more efficiently as well.
If you're not actually sitting with the person that you're flying with, I agree this probably isn't okay in most cases.