To start a relationship that has a defined end date; e.g., one of the people is moving soon.
"I hear you started dating some new girl."
"Yeah, but she's moving across the country in a month, so we're planning on breaking up."
"A little expiration dating, eh?"
When a woman is past her prime and looks it, but still tries to present herself as young and desirable. This might mean that she uses make-up tricks, botox, lip injections, etc. to appear more youthful to attempt to shave years off her age.
Many celebrity chicks over 40 are past their expiration date, but spend a lot of money trying to look like they are 5 - 10 years younger.
Pajama casual is a term used when working from home and preparing for a video conference. All business above the waist and your pajama pants down below.