In episode 3 of Tsukimonogatari, Araragi said "It's not that uncommon for the collection of unpaid tabs to all come at once lately." I checked another set of subtitles, and found that those gave "Lately, it isn't so strange that a bunch of unpaid tabs come knocking all at once though."
Honestly, I'm confused and not sure "unpaid tabs" means. Is it a joke of some kind or what? I'd like some help and explanation, thanks.
At a bar, you can put something 'on your tab', which is a way of saying you'll pay it later (usually next time you come to the bar) which when you do pay later, can be known as 'collecting a tab'
What Araragi is saying is that all the things he has been putting off have come back looking for resolution at the same time.
A big plot point of Tsukimonogatari revolves around the fact that Araragi has been dipping into his vampire abilities ever since the events of Kizumonogatari that turned him into this half-vampire, half-human... although more human than vampire.
You've seen him using his vampire abilities throughout the series so far, such as when Hitagi staples the inside of his cheek or he fights the monkey spirit possessing Suruga in Bakemonogatari, and when he fights against Kagenui in Nisemonogatari. These are just a few examples.
Every single one of these times, this human was drawing from these inhuman abilities to perform inhuman things. In the time of this story that Tsukimonogatari takes place, it became apparent to Kagenui and Ononoki that this was a problem. If he continued to draw upon these vampire powers like that, it's likely that he could turn into something no longer human.
This is the basis of his "unpaid tabs" line. As Toshinou Kyouko says in their answer, a "tab" refers to a running bill at a bar. At a bar, you can choose to not pay for your drinks, and instead leave a "tab" that you will pay at a later point. Here, the "unpaid tabs" are all the times he used vampire powers. However, at some point, these tabs do need to be paid - namely, with his humanity.
Basically said, it's Araragi (and Nisioisin, the original novel's author) using a metaphor.
