Similar to "dropping a duece". Its where
you sit down on the toilet to have a poo , but it may take
awhile, so you typically
bring in work to do like a laptop or a book
or magazine; and since you don't want to divuldge that you're crapping when someone
calls you, you tell them that you're having a sit-down meeting instead.
"Hey Dude, how's it going?"
"Cool, man. I'm just having a sit-down meeting
and I'll call you back."