This is unlike Garak at all. He would never close for the week. What about all his customers?!

I have to respectfully disagree (also I bloody love that we are debating the psychological nuances of a fictional character from a show that ended, what... 25-ish years ago?)

I can't recall, off the top of my head, Garak ever telling a joke per se. He got his enjoyment out of subterfuge and misdirection - did he kill that ambassador or was he just a gardener, which was extra intriguing because earlier in the show you didn't really know what his previous line of work was, you just had suspicions. But if he did then it was in the past and it was an assassination in line with his job. He can get off on hinting about that kind of thing, and his colleagues can go along with it, because it was in the past and it was a professional hit, so the people around him don't have to worry about him doing the same to them. It's like listening to vets tell war stories, even if they killed a whole lot of people you know it was for their job and a good cause. They can even joke about it, because it's in the past.

But in this joke it's implying that he's just going to kill somebody at random, because he hasn't decide who that person is going to be. He isn't in the Obsidian Order at this point, so he's not assassinating to protect Cardassia. In Pale Moonlight he assassinates, openly even, but it's for a good cause and it is indirectly sanctioned by Sisko. His style of humour was basically masterful (and kind of dark) trolling, not blunt "har har I'm going to kill someone" jokes. I guess you could infer that he might be killing someone in a professional context, and maybe there are multiple targets so he hasn't decided which target to kill yet, but obviously it's a short form meme so there isn't room that kind of context. As is, it feels like a poor caricature of who the character really was.

That said, the joke is still funny and I have no idea why I've typed this much about a fucking meme instead of working 😂