Okay, so at the Zoo or any theme park when you draw caricatures, drawing couples has many advantages. One, you double up on the money you get. Woot! Second, you typically will just draw faces which lets you play with the differences between the people sitting there, and third, its usually some schmo and a hot girl, so you play up how much of a Neanderthal he looks and cute and charming the girl is.
Disclaimer: This is a huge generalization and couples come in all shapes and sizes, races and creeds, so the pics here just illustrate my last point. Also I'll admit that I don't push the exaggeration to the point of insult, some of my colleagues enjoy testing the public to see just how far they make people feel about their insecurities. In the end, I just want them to laugh and buy my cartoons. With a large frame.
This guy really didn't want me to take his picture after I drew it and yes his head was HUGE!