Carrier

Someone who is sickly or contagious yet still goes out to social spaces, usually in absence of a mask or barrier to keep the general public safe.
They also tend to cough or sneeze without covering their mouths, and rarely wash their hands.

"I was so sick I could barely walk, but still went out with the boys to the party."
-"That's some serious carrier behavior."

i.e.: The sick person should have stayed home instead of potentially getting many unaware others sick.