Your parents wiped your ass. There’s no reason to be embarrassed about anything.

Just say it quick, like ripping off a bandaid:

“I need to see a doctor about a hemorrhoid that won’t go away.”

It’s not even in the top 1000 worst things kids have to tell parents. If you can’t tell them about a hemorrhoid, how are you ever gonna be able to tell them about the gay prostitute you accidentally knocked unconscious, thought you killed, and then tied up in the basement after they woke up while you were trying to bury them?

If a hemorrhoid is the most embarrassing story you’ve got, you have no reason to be embarrassed.