I still picture it going like this in the writer's room: So, uh, how can we make Toby's bachelor party awkward as hell?
Writer X: How about we have Simone call Toby and tell him she has an STD. And Emmett will be there too so they can get tested together and be reminded of the fact that Toby's best man slept with his ex-girlfriend while they were together.
Writer Y: Perfect! Yeah, no one will think that is weird at all.