It's good practice to spend 20 seconds washing your hands with soap and water and rinsing them well. Even assuming that you don't have a disease you can contact when you touch your...organ...handwashing is a good way to cut down on the transmission of bacteria and viruses and washing after urinating is a good reminder to do it.

Washing well after defecation should be a must. Diseases from polio to typhoid to cholera to E.Coli to are spread by fecal material -- if not yours, someone elses. And don't tell me you don't shit on your hands, either!