One did not become the most successful bard on the continent without learning to play to one's audience. To flatter a patron, as it were. To lie like a rug, bluff like a cliff, and do it all with a shamelessness that might be the envy of the continent's finest whores, one might say. Jaskier had learned quite a lot in the days since his best trick had been needling people into throwing bread at him for a quick meal. All that to say that the bard was in the private domain of a vastly more powerful wizard, behind stone walls and enchantments most foul, and considered himself to have Barry right where he wanted him.
The wizard had never actually asked Jaskier if he would like to come back to his unnecessarily tall tower, but that was about what Jaskier had expected. When Barry announced that they were going, Jaskier had quite convincingly pretended to be delighted. He had even talked the Wizard into allowing him to grab his possessions from the back, as of course there was the possibility he would not be returning for them. A possibility that had Barry going slightly starry-eyed as he leveled what he clearly believed to be a surreptitious glance at Jaskier's ass. The pompous moron went so far as to let him leave a private note, specifically for Geralt of Rivia, actually believing it was some sort of denunciation.
This level of stupid was unfortunately familiar to Jaskier from his upbringing in the nobility. Provincial stupid could include such creative and entertaining outlets as putting weasels down your pants for fun* or believing witchers had the power to move backwards in time to erase their mistakes. The sort of stupid that came with privilege was considerably less varied; powerful people who believed themselves infallible and untouchable, and acted accordingly. A great deal of the time they were right about the latter, but if there was someone (say, a certain bard) who was possessed of enough of the other type of stupid to try, they might find themselves surprisingly vulnerable.
The bard not only had a great deal of that to be working with, he also had a demijohn of vodka. He had been saving it for when he "coincidentally" met up with Geralt, but this was surely a most noble cause to put it towards. Plus, he might be able to make off with a small selection from Barry's cellar as recompense. Still, no sense counting his wine-bottles before they were stolen. That the stuff was strong was the important point. It was the very best that Oxenfurt, with all its academics, artisans, and bored students, had to offer.
Barry had been all too happy to pose, and preen under outrageous praise, and be served drinks with a great deal of berry juice, honey, and preserves stirred in. Which might conceivably mask exactly how much alcohol might be also be in them. It was a little known fact, but one of the infamous math finals of Oxenfurt involved calculating the exact amounts of alcohol that would be needed to reach different levels of inebriation with varying weights, heights, and genders, of all the known races. Jaskier was still rather good at doing it in his head, and had used it more than once to pull a 'let's not and say we did' with someone's blacked-out self. No lovemaking was so gratifying as what people could tell themselves they had performed. It was also useful to figure out who wouldn't be able to recall the perpetrator of a well deserved punch to the face in the morning. This would be a little bit of both.
End Note: *This is an actual thing. No, really.