Any time that a cock shoots it’s cum for me, I say thank you. It’s a reflex for me. If I didn’t, I’d feel like I was insulting him for cumming.
Whether his cum is perfectly clean, or he’s a full blown aids top with every std possible, I will always smile and thank him for his cum. I served my purpose, and he may have worked hard to cum just for me (for some guys, it’s a chore... enjoy your youth lol).
I think if you’re there to make a man cum, you should thank him when he does cum. And hey, if you get knocked up from that cum, you’ve thanked him in advance for that!