15 days, 15 in game days, that's how long I managed to keep ownership of one horse, became quite fond of him also, saved my characters life a few times, either by killing or riding hard to escape.

Then this fateful day we happened on a fort occupied by bandits, we were just going to go around the fort to avoid confrontation, I only have light armor and one handed is still a little rusty, no chance, the bandits had moved around to the rear and also in front, I suppose in hindsight getting off the horse was a foolish move, but I did not think to sprint the horse at that time, so now I'm battling 3 bandits, an archer and a pair of two handers, as if this was not enough a pair of ice wolves decide to join the fray, fortunately for me they attacked the bandits first, with the help of the wolves I took down two of the bandits only to see the third put a last arrow into my horse and it fell, I saw red, killed the two wolves because they were now attacking me, then the archer, but my revenge was not over, I went through the entire fort and massacred every bandit I could find.

Oddly enough I would not normally win in those circumstances as I put most of my skill/perks into sneak and archery, but nothing was going to stop me getting revenge, after the last bandit fell, I felt no satisfaction as my horse lay dead outside.

So as the thread title states, have you lost it?, tell us about it.

I have bought and lost all 5 of my horses.....me and cliffs just seem to find each other. Thats why I was so happy to find Shadowmere (well I just love him anyways)....turns out he can die but thankfully respawns.

Hah, your vengeance was well-deserved IMO.

With me, I just one day got frustrated with the vendors running out of gold and decided to mindlessly slaughter everyone in town.
=p
I didn't save it of course.......but it was still fun!

Shadowmere is a tough bastard indeed

I often find myself losing it on a housecarl after they've goten in my way whilst decorating or just relaxing in my fine home. At this point I kindly tell them I need their help, lure them to a remote and quiet area and begin chopping limbs. Its quite satisfying watching their bodies fall, maniacally laughing, and knowing none will be the wiser and I can finally get well rested without someone constantly watching me sleep (and constantly standing up and then sitting back down in the same fracking chair LYDIA!).

I was up against a bunch of necromancers. Every time I put one down, another would rise from the dead and together they would send me off to meet the Master of Trials (i.e. die and reload). It was infuriating. I have to give myself credit though. The LCD screen, on which this played out, remains unscathed. In any case, those frustrating necromancers provided me with the means for revenge, in the form of a black soul gem; the kind of revenge that is never over. She still serves me now. Every time my sword is battered by a shield or defiled by the blood of some foul beast, there resides her soul; equally battered by the enemy shield; equally defiled by the blood of some foul beast. I hardly think her fate well deserved, and I think it is this which makes the revenge so sweet.
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I too lost a horse, and I too had grown fond of that horse - but it was my own fault. I neglected to scout the exterior of a barrow before going in. And when I came out, overburdened by all the loot, my sweet carniverous horse (so fond of sarber cat and dragon flesh) had been slain by a bunch of trolls (who'd made themselves scarce when I was outside). It sounded somehow familiar - reminiscent of another time and place. It might have been my fault, but it pays to never leave a troll standing as there is always more mischief for a troll. And so it came to pass that I hunted them down, one by one, and perforated them slowly with bow and arrow instead of despatching them quickly with fire and blade. Admittedly it was the blade skill which was in need of practice so perhaps I did act out of revenge in this case - but none is so sweet as the ring of my sweet necromancer (who so infuriated me in the process of trying to kill me) as she clashes agonisingly with the armour of my most formidable enemies (in her present incarnation of a vampiric sword).
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How wickedly unjust.
How strangely appropriate.
How utterly satisfying.

Just recently, I got jumped by 3 Thalmors and 3 horkers at once. Faendal was doing his best to handle it all, as was I, but I kept getting hit with a spell because there was a mage around. I was dealing with a melee or archer guy and keeping an eye on an angry horker, and throughout, zap...zap...zap....finally, the mage ran up to me, and I just lay into him, with every hit, going, "Would. You. F*cking. Stop. That." It took a surprising number of hits, with me saying each word as I went along, and I hit him again after he went down. I then turned on a horker, hit him, and he went flying through the air. I subsequently found another had landed on top of one of the Thalmors. It was awesome.

But yeah, mages tick me the heck off. I am almost full melee. I use shouts, and I only we magic if I need it, like for non-normal damage things. Not surprisingly, I must rely on others to lure dragons down.

I actually let my horse die because it was a hindrance.

But no I've never lost it, because as an assassin I am cool and calm, in both my personality and in doing my job.

I punched my horse

When I first arrived in Solitude, I had every intention of joining the Imperial Legion. And that's when I stumbled upon that Stormcloak being executed. I watched in horror as the townspeople booed him and the axe chopped his head clean off, at which point I made a knee-jerk decision to side with the Stormcloaks instead. I reloaded to my last save and mowed down every single guard that got in my way the second I stepped into the city. My bounty must've racked up to, what, 13000 septims? 14000? I didn't see where the prisoner went, but I bolted and made a beeline for Windhelm. I'm pretty much banned from Solitude now.

That reminds me, there is some well deserved payback that I owe a certain Thalmer offical...
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...and I have a key to the back door!

I tried many times to save that prisoner, eventually I tested to see if it was possible via console commands, as it turns out it isn't. Even if saved the prisoner will merely stand there, no new dialogue, if you try to save him without cheats all guards will instantly become aggressive towards him and perform a one hit kill.

As for my horse... I misjudged the distance of a jump, he valiantly gave his life to cushion my fall.