I once dropped the radioactive barrels on Cottonwood Cove without freeing the slaves only to remember about them about an hour later and felt so bad I went and reloaded my save. (also sorry if this already exists)

See Dogmeat die because i forgot him.

And the rest of all the bad things i did dont bother me much.

I killed that hobo ghoul in freeside for little to no reason. I just went up to him and blew his brains out.

Telling the slaves in the cage that their safe to leave in Cottonwood Cove when I didn't disarm the bomb on their necks.
They were so close then BOOM! Game over...

That one time I told a lie to Milly about Wild Bill. I didn't think she was going to faint...

One time, I was playing with enclave commander and had a huge BoS squad following me, and went into Rawr's cave. We killed him, lost three of my paladins, and then I had to open up the entrance with the warhead...I didn't realize about six or seven of my guys were stuck under the rock when I blew it up.

Spoiler:

Legitimately felt like I would get a court-martial or something.

what!? hell no i am a legionnaire, legionnaires dont have dignity so nope

I killed everyone in Freeside... I regretted doing that because I was like, great what am I going to buy now?

I had Enclave Commander on, similar to the person a few comments above me. I had the same squad I'd had since the very beginning and they had survived for so long going and saving wasteland citizens from bandits and raiders. I added Cazaclaws to the game, my soldiers wouldn't retreat back fast enough and some of them died. Only 3 of us remained.

Well i test all available options and whe i feel bad i go bakc in the save, but for me the thing that made me feel extremely bad was bothering the ghouls on the history museum by reprogramming cerberus

I only did this as a test to see what would happen. I told Willow to leave. This was also around the time when we became more than friends, so it REALLY hit her hard. When she left, I was like "There goes my babyyyyyyy". Good thing I saved right before that time lol.

I may or may not have killed every child at little lamp light

Because I am a completionist, I did a super evil playthrough of Fallout 3. The one thing that made me feel like a genuinely horrible person was helping the slavers capture that girl from Little Lamplight. I immediately had to swap to another save file and bomb the shit out of Paradise Falls to purge myself of the feels. I still cringe a little at the thought of that quest.

A lot of the follower endings from New Vegas had a "damned if you do, damned if you don't" feeling about them. Veronica and Lily really didn't have good endings, no matter what route you chose. There's something about people being doomed to unhappiness no matter what that bothers me. I'm not a person that has to have a happy ending all the time, but at least one moderately positive epilogue would have been nice.

Lastly, I always felt a little guilty with having to make Marcus wait outside Vault City all the time.

Because I really like dogs and In one of the mods i have been playing has a main quest where you have to kill a guys dog to make him talk and I really wanted to finish the quest so i threw a frag at him to make it quick and painless.. Up until today I still feel guilty about It even though its was just a in-game dog..

On my first play through after I had finished talking to doc Mitchel I went around his house and stole all his stuff, but then after I felt bad because he had just patched me up after being shot in the head.
My character: 'Thanks for patching me up doc, I'm just going to see if there's anything useful in this house of yours'

In my first game in New Vegas, I choose the NCR at the end and when they ask me to kill the King I obey. But after this, I didn't realize that I've killed everyone in the King's school and I've regretted deeply what i've done.

I killed every single character in the game...well except the children...felt pretty bad about that, I just thought I'd try it and see if it could work

When I got the crimson caravan contract to buy Cass out of her own company, I was thrilled because that meant she could finally join up with me and be my packmule! I want to the mojave outpost and I convinced her to sell her comapny to the crimson caravan. And indeed she was willing to pair up with me .

When I got back on Freeside, I accepted several contracts from the Silver Rush. One day Gloria Van Graff told me I did a good job and should speak with Jean-Baptiste Cutting for more work. I did, and he told me he wanted to have a nice talk with Cass. As naive as I was, I told him I had her with me..

Then He became all hostile to Cass, and I knew what was comming.. Jean-Baptiste talked to me once more (I don't know the options anymore) and with the knowlage that there are around 6 thugs in the shop, I had to tell him he could go ahead en kill her.. I felt so bad after I saw that puddle of goo Cass transformed in

R.I.P Cass, our ~30 min adventure will never be forgotten.

Killed Dogmeat with a explosive by accident in Fallout3. Well, to be honest, it wasn't really an accident, just bad AI programming done by Bethesda, Dogmeat always charge head on in the line of fire, or in my case, 5 plasma mines.

I did a negative karma playthrough...I shot EVERYBODY I came across. Seriously a downer for a playthrough in either game...and I thought siding with the Legion was the worst I could do haha...Nope.

I hated my character, and had to start a new game. Easy Pete wasn't bothering me, but he got it any ways, and Old Lady Gidbson I just plain felt terrible about. Not to mention her dogs. I feel bad now...Time to go kill some Raiders and Legion parties.


EDIT: I forget that some npc's are essential, but the GECK and a mix of evil mods fixed that haha...