Engaging in sexual acts with three or more people where at least one participant is a transvestite of African heritage. The number of cars in the "jungle train" represents the number of people involved in the sexual act.
For their 10th anniversary they went to Vegas and rode a three-car jungletrain.
A 3 way between 2 males and 1 female with the male in the middle. When you're about to penetrate you yell "All Aboard!" And when you're about to cum you say "We are now arriving at your destination."