One day, a man wakes up with a red ring around his penis.
He can't figure out what it is, so he goes to the doctor.
The doctor hands him a tube of cream.
"Here. Put this on and the ring'll be gone within the hour," the doctor said.
The man drove home, put it on, and sure enough, the ring was gone within the hour.
But then the next day, he woke up and the ring was there again.
He goes to the doctor, and the doctor hands him the same cream, which he puts on.
The ring vanishes, only to reappear the next morning.
This goes on for a few days before the man finally asks,
"Doctor, the cream you're giving me takes care of the ring around my penis, but then it comes back in the morning.
What's the stuff you're giving me?"
The doctor hands him another tube of it before replying, "Lipstick remover."