Yeah it's not selfless to enter a situation in which one person (you) will absolutely 110% die, when there's someone right next to you who is 100% immune to the very thing that will kill you.
In fact, I would say that anyone in that situation who wouldn't immediately let everyone know "hey I'll be perfectly fine doing this, so stand back I got this" is kind of a piece of shit.
It's literally "I would suffer no I'll effects by doing this, but it wasn't built by MY dad so go fucking kill yourself with it, tiny humie"
Argh that was so frustrating-- His story seemed so tailored to help you specifically with that problem, and I felt so clever for trudging across the map to get him for that situation... It felt like a prank when he's just like "oh great idea but no because reasons."
Which game had the super mutant who called your deary and dressed like a grandma? I know that's a real memory but I'll be damned if i remember... I wanna say NV