What's annoying:

Doing something perfectly normal on Insanejournal, no warnings that the site is down on Twitter, and getting a 500 Internal Server Error:

===
Internal Server Error
The server encountered an internal error or misconfiguration and was
unable to complete your request.

Please contact the server administrator, webmaster@insanejournal.com
and inform them of the time the error occurred, and anything you might
have done that may have caused the error.

More information about this error may be available in the server error log.

Additionally, a 500 Internal Server Error error was encountered while
trying to use an ErrorDocument to handle the request.
Apache/1.3.37 Server at insanejournal.com Port 80
===

But what's doubly annoying:

Trying to REPORT this error to the e-mail address given, and discovering that:

===
This is an automatically generated Delivery Status Notification

Delivery to the following recipient failed permanently:

webmaster@insanejournal.com

Technical details of permanent failure:
PERM_FAILURE: Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 5.1.1 <webmaster@insanejournal.com>: Recipient address rejected: User unknown in virtual alias table (state 14).
===

If Squeaky prefers not to get e-mail messages reporting site errors, then the error page should say so.

It's just annoying to be presented with an e-mail address and invited to report an error, only to discover that the e-mail address is not in use.