結論、以下のコマンドでインストールできる

sudo pip install awscli --upgrade --ignore-installed six

以下、経緯

AWS CLIをインストールしたい

ここを見てインストールをすすめた

curl "https://bootstrap.pypa.io/get-pip.py" -o "get-pip.py"
sudo python get-pip.py
sudo pip install awscli

謎のエラー

Found existing installation: six 1.4.1
    DEPRECATION: Uninstalling a distutils installed project (six) has been deprecated and will be removed in a future version. This is due to the fact that uninstalling a distutils project will only partially uninstall the project.
    Uninstalling six-1.4.1:
Exception:
Traceback (most recent call last):
  File "/Library/Python/2.7/site-packages/pip/basecommand.py", line 215, in main
    status = self.run(options, args)
  File "/Library/Python/2.7/site-packages/pip/commands/install.py", line 342, in run
    prefix=options.prefix_path,
  File "/Library/Python/2.7/site-packages/pip/req/req_set.py", line 778, in install
    requirement.uninstall(auto_confirm=True)
  File "/Library/Python/2.7/site-packages/pip/req/req_install.py", line 754, in uninstall
    paths_to_remove.remove(auto_confirm)
  File "/Library/Python/2.7/site-packages/pip/req/req_uninstall.py", line 115, in remove
    renames(path, new_path)
  File "/Library/Python/2.7/site-packages/pip/utils/__init__.py", line 267, in renames
    shutil.move(old, new)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 302, in move
    copy2(src, real_dst)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 131, in copy2
    copystat(src, dst)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 103, in copystat
    os.chflags(dst, st.st_flags)
OSError: [Errno 1] Operation not permitted: '/tmp/pip-Rj2bkf-uninstall/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/six-1.4.1-py2.7.egg-info'

エラーを見てみた

Found existing installation: six 1.4.1
(既存のインストールが見つかりました)

sixとかいうのが入っているらしい
six:python2系と3系の差異を埋めてくれるユーティリティライブラリ

すでにいろんな人が書いてた

ここまで書いててわかったのですが、すでに他の人が書いてました
Qiitaとか、SixのエラーでAWS CLIをMacにインストールできないとか
でもここまで書いちゃったんで初投稿も兼ねてメモしておきます〜