Also doubt i'll ever
Spoiler
blow up the Citadile since it makes the BOS hostile.
Well, before the final decision, save, then just do it. It's not really worth it, IMO, just for one faction to be hostile and one weapon. So then you go back to your save and pick the other option. Then you can say you've done it :laugh:
A few things come to mind that I've never done. I've never taken the Bloody Mess perk, nor met Casdin. I have no interest in helping the Outcasts or doing that miscellaneous quest. Outcasts are sort of useful as distractions while I run in the opposite direction away from that Deathclaw or Enclave patrol.
Other things I haven't done are pick the worst, most nastiest dialogue options when chatting to other NPC's. Even when playing an evil character. I either pick the friendly or somewhat neutral option. I did try it once with Reilly, but her response made me feel bad so I reloaded and picked another.
On the other side, I've blown up Megaton, enslaved everyone on the list (and they made it), enslaved Bryan Wilks, convinced Bumble into going on an "adventure," gave a junkie some drugs so he overdosed and died, didn't help Mei Wong then later enslaved her, pushed Mr Lopez, sneaky snipe friendly NPC's, plant grenades in pockets of Tenpenny guards, Rivet City Security, Lucas Simms, random other townspeople. Choose the other option with wasteland captives (take the supplies), but have rarely left them there.
All sorts of things. I'll try anything once, except that perk and helping the Outcasts