eavesturbate
to get off while listening to someone else's messy and probably very loud sex
He eavesturbated through the floor and got a full-blown erection when he heard his dad's loud and messy sex.
She eavesturbated from the bathroom and started crying when she heard her brother's whole family having sex at the same time.
He eavesturbated through the window and was so turned on he started peeing on the lawn.