There are some eye-catching new billboards around town this week. They show silhouettes of people with these words written over them: “Tinder, Chlamydia, Grindr, Gonorrhea.” The makers of the dating apps Tinder and Grindr are not happy. Tinder is demanding that the AIDS Healthcare Foundation, which created the billboards, take them down. Grindr cut business ties with the nonprofit. But the Healthcare Foundation says research is on its side in showing a link between so-called hookup apps and STDs.