Rubbing puts you at risk for HPV, syphilis and herpes. These are all transmitted by genital skin to skin contact, and symptoms do not need to be present in order for them to transmit.
There are many strains of HPV that don't ever give you actual visible warts.
Herpes can be transmitted without symptoms due to asymptomatic viral shedding, which is when the virus is present on the skin, but there are no symptoms.
With syphilis, there does need to be a sore present.
I can't give you odds - probably not that high, but definitely possible.