Hacker News Reader

It would be neat if the code also applied to the username in the top right so I didn't have to make a spammy comment to see what it gives me. ;)

Just replace the '.hnuser' bit with '.hnuser, #me'

Just F12 and manually edit some username, after that re-paste the code and you will see the avatar.

The other way is to just navigate to your own profile page and apply the script there.