This happened between my dad and me, last week.
I was home alone. My dad wasn't going to be home for about two hours. I was on my bed naked and jacking off. My dad must have gotten off work early because he walked in on me. I didn't even hear him come into the house.
I said that I was sorry for doing it, but he told me not to worry about it; in fact he said he wanted to help me. So I said, ok. Then he started to take off all of his clothes and he then started to get hard.
He got on top of me and grabed my dick and started to go at it. Then I said, 'Oh, my god, I am going to cum.'
Then he said, 'Don't hold it back, Son.
I came all over his chest. Then, I returned the favor. We now agree to help each other out whenever we want.