Imagine person A of your OTP is busy on their laptop/computer at their desk and person B is feeling kind of horny. When person A waves person B off, telling them they’re busy, person B gets underneath the desk and starts caressing person A’s thighs and crotch (optionally: whispering how much they want it right now, if that’s in-character). Person A gets turned on as well and person B goes down on person A. Eventually person A gives in and pulls person B up from underneath the desk, resulting in a hot messy scene on top of the desk in the end.
Imagine your OTP having a late night cram session for finals. Person A starts becoming very tired and is dozing off, so Person B forces them out of their chair, and gets them to dance with Person B to get the blood flowing. (Bonus points if they get carried away with the dancing. Bonus points if Person C joins in as well.) Finally, they realize that they need to get back to their studying. (Optional: Not long after they sit back down they already feel tired again.)