"You've got..."

"...herpes!"

It's a good idea, but man...can you imagine getting an e-card from them? There are so many delicious possibilities for doing that tastelessly.

"Ever wondered what it would be like for it to burn when you pee?"
"Hypothetically, how would you feel about oozing sores on your genitals?"
"Clap on!..."
"After a night of freaky sex, I hope you're well rested/But just as a thought, you might want to get tested..."
"We want to give you oral...antibiotics!"
"Herpes: the gift that keeps on giving..."
"You've got three letters. The first is H, and the last one is V. Is the middle one P or I? Find out!..."
"Ever heard that song 'Tainted Love'?..."

Etc...