Knocked the powerlead out of one of our main Virtual host machines, not really my fault as we SHOULD be buying servers with redundent power supplies especially when there hosting multiple machines as VMs
I just hung around in the server room for a few mins until everything had come back up, and pretended to be none the wiser when asked if the internet had gone down (surprisingly no one else noticed a thing even though 2 DCs, 1 Main apps server, a print server and a proxy server all went down - must have been a lot of slackers that day)
Only other major problem ive caused was when our main 4108 core switch was close to capacity, i made a change on it (most likely configuring Vlans at the time) next thing i know i had lost my telnet connection and half the network is no longer working