Diseases You Prolly Have:

Herpes:  Up to 80% of Americans have HSV-1 (oral herpes/cold sores) which can be transmitted to the genitals.  About 1 in 4 Americans has HSV-2 (genital herpes)

Mono:  Infectious Mononucleosis (the Kissing Disease)  is cause by a virus known as Epstein-Barr Virus (EBV).  95% of adult Americans age 40 and older have already been exposed.

Hepatitis A: It is estimated that nearly 80% of Americans age 60 and older have been exposed to Hepatitis A at some point in there lives, and may have never become aware of their infection.

HPV:  Human Papillomavirus occurs in about 50% of sexually active males and 75% of sexually active females, many infections go unnoticed.

http://www.plannedparenthood.org/
http://www.cdc.gov/
http://your-doctor.com/healthinfocenter/medical-conditions/infectiousdisease/hepatitis.html