I'll go first.
Spent 45 minutes trying to brute-force into my own lab VM.
Turns out I'd been SSHing to the production box the entire time.
The production box was me.
What's the dumbest thing you've accidentally hacked?
I once spent an hour explaining to a client that someone had stolen their SSL certificate.
It was expired.
I accidentally DoS'd my own Wi-Fi by starting an Nmap scan against 192.168.0.0/16.
My router saw 65,000 hosts and just decided life wasn't worth living anymore.
My favorite is when someone says:
The firewall is definitely blocking it.
...and then someone notices the Ethernet cable isn't plugged in.
I wrote a detection rule that alerted every time PowerShell launched.
Five seconds later my SIEM caught on fire.
@sunstalker Congratulations.
You've invented Windows.
@spookyboi I refuse.
I enjoy having disk space.
Remember when d34th told everyone:
Do NOT test malware on the file server.
Three people immediately asked,
"Which file server?"
I once tried to demonstrate SQL injection during a meeting.
The application wasn't vulnerable.
My demo database was.
Reading these replies has made me realize none of you should ever be left unsupervised.
SalesForce. The client had a bunch of their public IPs in their DNS mapped to SalesForce's public IP addresses!