Imagine your OTP is out on an all-day road trip together and Person A has had to pee much of the time, but doesn’t tell Person B until they’re absolutely bursting. Person B, who has a desperation kink, takes pity on Person A and pulls into the parking lot of a bar. They walk inside, asking the bartender if their lover could use the restroom. The bartender replies that only paying customers may use them. So person B brings Person A inside, and they order some nice cold lemonades to drink.
When person A finishes, they ask where the bathroom is. The bartender responds that the bathroom of their gender is out of order. Desperate, Person A runs into the opposite bathroom to find only a urinal is installed.
Grinning to themself, Person B steps into that bathroom and guards it so no one else can enter it. Person A can’t take it anymore so they begin to relieve themself all over the floor, making Person B hard.