I was already familiar how to reset the entire head of my git repositories to a desired state, but what if I needed to revert the changes in one specific file which I had managed to bugger up while keeping all my other changes. The only reason this was hard because my brain is still slightly working in subversion language:
git checkout filename
so just check out the version of the file you want. This will land you in trouble if you have a banch with the same name as the file, in which case you can do:
git checkout -- filename
