I am one of the poor souls who have never witnessed it as it happens.
And it's a double shame because she was one that would give excellent head, and would ALWAYS swallow, unless there was a specific request for something different.
The husband of a married couple my wife has partied with quite a few times used to chat with me on computer, and would brag about getting head from her.
One time was his wife and my wife taking turns on him.
I listened to my GF fuck and suck over the phone on one occasion. That was sizzling hot!
She was fucking a friend of hers; I know the guy but we're not friends. So, in addition to them making out and touching, I listened to them fucking, and him telling me he had his fat cock in her pussy. He then ordered her onto the floor, and fucked her in the ass! I don't know if he knew, but that was the first time for her. He pulled out before he came, and my GF had no problem doing ass-to-mouth, so I listened to her suck him off and swallow his load. He finished by eating her pussy, because he loved her squirting in his mouth, so I heard him make her do just that!