I'll start:

"She's been fucking him for years."
(Either a great longterm provider-client situation or outrageous spousal support payments.)

I'm paying by the minute"

I don't know. I haven't been here in a long time. I come to check if I understand the jokes or not.  
I think I understand this one. Is this even a joke?

The short sentence: “I’m fine.” The volume and the intonation are the keys here.

1. The provider, when you ask her if she’s getting tired as she rides you in Asian cowgirl.

2. The wife, when you note that she’s been moody, and ask her if she’s upset with you over something you said or did last  
     week (month, year, etc.)

END OF MESSAGE

.

It's funny.