The dumbest thing you ever did to your stereo?

I was just curious about other peoples horrow stories. A few months ago, I disconnected my preamp and inserted another preamp. When I turned the pre on there was a horrific screeching, high-decibel, other worldly noise eminating from my new B&W diamonds...honestly, it sounded like an off-tune Scottish bagpipe army on steroids. The house shook. My heart was pounding and I quickly ran to the wall outlet and pulled the plugs. I just stood there in shock...just like when you just miss getting into a car accident. I was sure I damaged something...but alas, everything is alright. Because I dismantled the preamp so fast I still don't know what the hell I did. I'm thinking I may have mistakenly misplaced the interconnects or something. Stupid but lucky.
I heard that bare wire was superior to bannana's and spades, so I stripped the speaker wires and connected them up. Unfortunately, the stripped section was too long and I crossed the wires and blew out one channel of my amp. $300 later, I put the bannana's back on:)
AMP OFF before preamp off, ALWAYS!
Broke a Koetsu. Beers and vinyl don't go together ...
" When I turned the pre on there was a horrific screeching, high-decibel, other worldly noise eminating from my new B&W diamonds"

"Because I dismantled the preamp so fast I still don't know what the hell I did."

That's easy. You left that Celine Dion disc playing in your CD player.
Played frisby with woofer having a rotted surround. One day before learning that speakers could be reconed and that manufacturer had sold last original equipment replacement woofer one month earlier. Ouch, ouch, ouch.
Tube rolled 4 times with NOS McIntosh originals, Telefunken, Amperex, GEs and Mullards trying to tame my C2200 McIntosh Preamp of its shrill upper end. Constantly bought NOS and quickly resold at a loss on A'Gon because everything sounded harsh despite claimed warmth of those tubes and preamp. Was just about to send it in for warranty work when one day while sitting trying to listen I remembered that the C2200 had a treble dial - which I'd forgotten about since none of my equipment has had it in the past 15 years. So, I walk over to the Mac to turn down the treble from neutral and discovered the dial turned all the way up.
Then remembered my 2-year-old grandson had been left in the listening room unsupervised for a while just before it happened. Musta had a lot of fun playing with the cool dials. Turned the treble dial to neutral, everything sounded great. But audioplila nervosa set in again and the tube-rolling bug hit again. But now I am happy. Poorer, Chagrined. But happier. My son will never let me forget it.
I attempted to drive a set of Infinity RSIIs with a Yamaha M2.
please note the RSIIs could and would drop down to 1/4 ohm and the M2 is only rated for 8 ohms. It was like having Mohomad Alie and John Frazer in the same room. The amp was trying to destroy the speakers and the speakers were trying to destroy the amp.needless to say I was very upset.
I carefully clean my first pressing of Gaite Parisienne, set it on the turntable to play, lower the needle, then go in to take a shower (with the door open). Shortly later the music is interrupted by Zrrrip! Zrrrrip! Zrrrrip!

I leap out of the shower and rush naked and dripping to the turntable. There is my daughter's cat, sitting on the shelf, batting the tonearm back and forth with its paws...

The cat lived. The record didn't.
Do headphones count? I managed to ruin a pair of vintage Stax Lambda Pro Signature earspeakers by trying to suck out the last few crumbs of degenerated lining foam with a vacuum hose. Not a good thing to do for mylar diaphragms. No siree.
I don't really know where to start. Back before I knew anything about stereos, I had an old Mitsubishi system with BALLS of power. Well, I know it got freaking loud, and in HS, that's all that mattered right? Well, I got a second set of speakers and this system was like 20 years old, no A/B so I just tied the speaker wire together and BOOM I have 4 speakers instead of 2. Now the parties were even louder and it ran fine. I used this set-up for about 2-3 years perfectly fine (I know now, I was down to a 4 ohm load on an 8 ohm reciever). Then I was in the market to get a new stereo when I got to college, so, what did I do? See what it took to blow up the old amp before I got a new one. ANOTHER pair of speakers later (now we're down to 2 ohms for those of you keeping track at home). This ran ok for about a semester, then durring a rather extended party, it finally died. The power supply was too hot to touch.

Long story short, blowing up the amp for no reason was the dumbest thing I'd ever done, but I was impressed at how long it lasted before I finally killed it.

Now that I'm all grown up, I couldn't imaging doing something like that again, oh well, I was young and stupid and no real bills to pay. But I did come out with a lot of good memories
I rolled the 12AT7's in my VTL mono blocks. I put in 12AX7's by mistake. Other than sounding like crap and feeling like a dork, nothing bad happened.
How about prying the drawer open on a CD player because an import disc was inside and the player wouldn't give it up? yep.
I agree with the "beers and vinyl don't go together", the vinyl saw blade took my Schuer microridge V to worhthless, $225 for stylus.
So when I hear folks say they wish they were "18" again, I just feel thankful that I don't have to be *that dumb anymore. Yeah, I used a butter knife do it, so i wouldn't really scratch the player, whew.
Tried workin' on on old Garrard Turntable, back in '76. Had the flu, could barely see, and didn't properly brace the TT when it was on its side. Managed to bump it, tipped it cver, and put a 30 degree bend in the tubular tone-arm just past the counter-weight.

Went back to bed, rather upset. All worked out well. Had a new Kenwood KP-5022A D.D. Table the next week. Something about that Kenwood that I loved...really great table for its day!