

(despite my very clear “no, thank you, you know I’m really not interested in that with you or anyone else. That doesn’t sound fun to me as much as you think it should, so I’m not interested, but thank you for being honest about it so we could be entirely clear, now please stop commenting on what you want to do to me…”)
Respectfully, that’s far too many words. He said he knows you’re not interested, so everything after that is deliberate harassment. So if you’re comfortable with it, you should say “you know I’m not interested, now quit harassing me!”
I wouldn’t normally give this advice but since you’ve said you can handle physical confrontation, the direct route may work for you. You’re being too nice to a guy who is being zero nice to you. I also wonder if this guy is taking ace/aro the same way some guys take lesbian - as in, they see it as a challenge and think their magic dick will “fix” you. (Obviously you’re not broken).
As far as the guilty feelings, I get it - society trains us to care about others’ feelings more than our own. But try to remind yourself that he’s being deliberately offensive and it’s OK to be rude back sometimes.
As for the young guy, that kind of situation happens. It sucks but that’s life, and honestly, it’s good you gave a firm but kind rejection. I think you handled that one fine! I can’t tell from the story if he was hitting on you or just awkwardly trying to make a new friend, but either way, ‘no’ is a complete sentence. ‘No, thanks’ if you want to be kind. You don’t owe anybody an explanation.
Since you’re asking how to feel better about saying no, consider that these men (especially your coworker) aren’t taking the time to feel badly about imposing on you. They aren’t giving you due consideration, so why feel badly about giving them the same energy? Give yourself permission to not care. They’ll live.
Good luck!
Why so few times? The entire world must see!