lots of these are unnecessarily complicated:
> Oh shit, I accidentally committed something to master that should have been on a brand new branch!
# disappear the last commit and all changes from it
git reset --hard HEAD^
# make a new branch using the last commit
git checkout -b new-branch HEAD@{1}
first, you don't need to git-add before and after stash, stash will save the working directory and the index (as documented in the DESCRIPTION of git-stash(1)). but for a more logical way:
# disappear the last commit and all changes from it
git reset --hard HEAD^
# get onto the new branch
git checkout new-branch
# grab the stuff from what was on the old branch
git cherry-pick old-branch@{1}
git diff --cached