Currently my user page https://security.stackexchange.com/users/5133/curiousguy?tab=reputation contains:
<a class="youarehere" href="/users/5133/curiousguy?tab=reputation" title="reputation you have earned" data-shortcut="R"> <span class='bounty-indicator-tab'>-3823</span> Reputation </a>
-3823 is the largest absolute reputation change I have seen. I am not worried, my reputation graph seems to be mostly monotonic, but that is odd!
(I don't consult that user page often as I use the message box to see replies and events.)
I have seen only one "User was removed" event:
-10 May 14
-10 21:03 removed User was removed (learn more)