Flu

Flu is a running gag in The Petri Dish, especially because Thaddeus Euphemism is paranoid about catching it.

During the Flu arc, Thaddeus did get the flu, but he's never caught it since.

In one strip, when an intern sneezed, Thaddeus put on a Hazmat suit and cocked a gun because it was flu season and he hadn't been vaccinated.

In another strip, a lot of employees caught the flu, so Thaddeus, to prevent himself from catching it, wore a health mask, took off his shoes (not even the creator knew why), disallowed people to stand near him, and wrapped his torso up in bubble wrap, tying his arms to his body.

In another strip, a woman sneezed, but only because it was dusty. Thaddeus, however, thought she had the flu because it was flu season and sprayed her with a hose while wearing a hazmat suit.

In the Protective tank arc, Thaddeus put himself naked in a tank of water to protect himself from the flu and sprayed water on a man who did have the flu.