Why does talking about sexuallly transmitted diseases always get akward?

So I sent this heart as a valentine to a friend of mine and it sparked the following conversation


Katelin: why thank you for the valentines candy heart

me: oh no problem, i want to share hiv with everyone. I <3 HIV

Katelin: yes, of course. Why not spread the cheer of HIV

me: exactly, the gift that keeps on giving

Katelin: ...until it kills you

me: ...yeah. I guess this is the one situation where re-gifting is ok.

me: speaking of sexually transmitting diseases, how was your valentines day?

She didn't say anything back...