A couple of years ago, a lady-of-pleasure I was seeing, had earned the nickname from her co-workers, of "Firecracker" because when she orgasmed, she went "off like a fire-cracker" and she could be heard throughout the building.
Well, one day we were having a good time and she had had one squealing orgasm with my tongue. Once she had settled down a little, as she was sliding onto me, she had the back of her hand wedged in her mouth. I asked if there was anything wrong.
"I don't want to make too much noise. There might be someone in the waiting room (next door to our bedroom" was her reply.
"Don't worry about it" I said, "You might give them some encouragement".
She giggled, and came back with "I'll have what she's having!".
Well we both cracked up laughing. As I laughed, my cock twitched inside her. This was the last straw for her and she started convulsing on me, laughing, squealing and crying all at the same time. Needless to say, this tipped me over the edge too. This wasn't just a 'happy ending', it was a 'hilarious ending'.
Aside: Viagra works by causing the production of Nitrous Oxide (laughing gas) in the blood stream which cause the peripheral (face, and penis) blood vessels to dilate, thus improving one's erection. So there is in fact a chemical basis for the relationship between good humour and good sex.