Boba and Vader are stuck together waiting for... Something. Maybe they're doing recon and Vader insisted he needed to see some things for himself, so Boba has to deal with an extra headache now. But they're here, everything is quiet, the target is asleep in a different building, and Boba is uncharacteristically antsy. Vader's presence alone is enough to put him off his game.
So what does Boba do? Propose match of holochess of course, "since it's going to be a long night and there's nothing better to do."
Vader's reply is his usual wheezing—perhaps a tad louder, like a snort or a scoff. The usual derision.
"Join me," Boba insists as he is booting up the game. "I've played far too often against myself to take any pleasure in it anymore."
"Each idle minute on the job will result in a thousand credit subtraction, so tread carefully, Fett."
"Hmm... there's plenty of more active things we could be doing, if idleness is ill-advised. In fact—"
"Fett."
Sullenly, Boba looks back at his game. Being in Vader's proximity like this had seemed rather spicy when Vader told him the plans, but he realizes now it is closer to disappointing than fun.
Vader simply stays beside the window, watching the device mounted on the wall for any changes in movement or heat activity.
Boba moves a pawn forward on the board, opening the back row of his pieces to better paths.
There are a few rare strategies he could apply to respond to this opening move.
He is thinking about each option, trying to settle on one that would be most unpredictable for both sides, when an invisible opponent moves a pawn forward two squares, meeting Boba's pawn diagonally.
Maybe there's still hope for this stakeout.
You won't see Vader physically look at the board until the moment there's a sudden "Checkmate!" and Vader turns around angrily, all "What do you mean checkmate?? There was no way you could have—"
—but Boba is just sitting there very smugly. He had only said the word in provocation.
"So you were paying attention, Lord Vader, and it wasn't just my holochess table gaining sentience."
Vader: >:U