A more sexually explicit version of, "You couldn't catch a cold", meaning that someone is not good at catching anything.
Wally was so non-athletic, he couldn't catch herpes in a whorehouse.
OR
Being pursued by bad guys: Can't you guys keep up? You couldn't catch herpes in a whorehouse!
OR
Being pursued by bad guys: Can't you guys keep up? You couldn't catch herpes in a whorehouse!
by GallopingSausage April 10, 2019