I got a few from back when I knew jack shit. And why I say I got lucky with some of my newbie fuckups
1.) Learn about keyloggers, want to try one out, download some random one off some site, run it(somehow managed to configure it properly) and walked away from the home computer. Cue later that afternoon dad hops on, 'hey what the fuck is this trojan.w32.blah?'. I look at the screen and voila antivirus caught the keylogger I downloaded. Lied out my ass and said 'I dont know but antivirus caught it so it should be fine in quarantine.' It worked, and later that night I hopped on and let antivirus have an exception for the logger. Worked smoothly for several months.
2.) Speaking of dad, one night I had just learned about network scanning. Thought Id try it out and decided to start off with a ~50,000 host random nmap scan with the works. Figure Id check in on it morning time, so I minimized it(didn't know about nmaps output options at the time). Not only did Dad get to it first, open up the windows, he actually googled the damn thing. Ensue huge rage fest as my dad only saw it as a 'hacker' tool. Didn't help that some airliners got caught in said random scan(oh boy did he browse through my results) and my dad worked as a civilian contractor for a naval base. You try explaining how hacking can be good when youre still basically a skid and barely know the ethics behind the industry to justify yourself
3.) Learn a bit about mitm(theme going on here eh?) and decide to try it out...at my local library. I waltz in, sit down at one of tables reserved for laptop users, log on to the wifi, then proceeded to fire up ettercap's gui. What happened next was 30 sweaty minutes as I try in vain to repair the network as the entire library internet access, even the desktops on the LAN, is entirely borked to all hell and back. Library workers are running around trying to fix everything, users are complaining, and I'm sitting there, noticing the camera pointed in my direction for the first time ever. Somehow managed to reverse my damage and stayed for an extra ten minutes to not look suspiciously frantic.