Well, can't say I've done much myself, I've modified a couple of el cheapo guitars, never did any damage except for my first electric. Japanese Jaguar-ish fender copy, single pickup, I took it apart to repaint it, wondered what that screw was in the neck. Grabbed a screwdriver and proceeded to turn it until it snapped...the truss rod, I later found out...
That's my only bad one, I've dropped a couple here and there but with no damage other than a scratch or three. But a couple have been damaged by others...
Austin TX, late 80's, I played on 6th street for a long time, guys always wandered up drunk and wanted to play, I usually managed to nicely tell them no and they would leave it at that One dumbass just wouldn't let up, PROMISED he would only keep it just a minute (yeah right, it usually takes me 15 minutes to get my guitar back and I'm trying to make a living here...), I finally gave in just to shut the guy up. He didn't get the strap completely on the bottom peg, let it go and my Epiphone hit the sidewalk face down. I grabbed quicker than he did and told him not to touch my guitar again. He started apologizing, I just told him to leave...NOW...The guitar buzzed badly the rest of the night, I had to re-glue all the support struts inside on the front, cost me 2 nights with zero income. It still sounded good, but I don't think it was ever quite the same. I've never found another one to match it...
When I bought my current Takamine acoustic/electric at a pawn shop, the lady I asked to get it down so I could play it was sitting on a stool eating lunch. It was hanging above her and instead of standing up, she stretched to reach it off the stool, just as I said NO! she bobbled it against two other guitars, broke a pencil eraser sized chunk out of the finish on front, a ding on the back of the headstock, and another ding on the binding on bottom front. They knocked $35 off the price for that...and another lady tried to claim they didn't do it, but the lady who did admitted it. It still sounds fabulous though
And finally...I have a mid 40's Electromuse lap steel a close friend gave me. Took it to a gig one night, before I started using a keyboard stand, and parked it on a guitar stand. After the gig I was wiping down guitars to put them back in the cases when my niece and the lady friend who gave it to me ran over to me shocked and said the bass player (and band leader) had knocked it off the stand. I ran over and it was lying face down onstage, he didn't even bother to pick it up...next time I plugged it in it wouldn't work, had to replace the original cloth covered cord and the capacitor inside to get it fixed. I really wanted to keep that cloth covered cord for the cool factor...I mean, how many people have a guitar with a 60 year old cloth covered cord in working condition? It's soldered directly onto the volume control, by the way.
And in case you are wondering, I now make sure I NEVER let anyone touch my guitars when I'm not in my living room. Almost got into a fight a few months ago when some jerk picked my guitar up and started banging on it in the music store where I worked for a couple of months. Asked him what he thought he was doing with my guitar in his hands and he smarted off...not a good idea...First thing he did was "Well, I let you play my $2200 Taylor"...it cost more like $1700 I think, and I replied "Didn't YOU hand it to me?" He refused to answer me so I repeated it...he finally said yes...I also knew he played his Taylor way too hard, was a crummy guitar player at best, kept trying to sing really loud and off key, after I told him both didn't sound good, basically a jerk all around. Never tried to finish a song for 2 hours, and kept trying to play country after I told him I hate country and play it only onstage when I have to. He played rock and blues too, or tried to, and never even tried to follow anything I played, then usually started playing something else HE wanted to play while I was already playing, trying to get him to play something together...basically a jerk...
So yeah, I've screwed up one of my guitars, but other people have bashed them around much more than I have, I never let people touch them any more.