How does one become victim of one's own Karma?

Karma is a concept older than Buddhism, however Buddha changed it a little bit.

In Hinduism for example, Karma is the action and you will suffer the consequences of your actions, the change Buddha did is that he said Karma is created by the mind, so thoughts can create bad Karma and bad actions (without intention) do not create bad Karma, so the focus changed from the real action to the mind/intentions.

The Vipaka (consequences) have nothing to do with habits, the more you do the more you will face consequences, however Karma is not created only because of repetition.

In your example, who does the bad action you suffer the bad consequences, not the victim that is probably paying/purifying a past Karma.

Karma literally means action or causality. The Buddha's doctrine of karma is that your own intentional actions determine your own results, and thus when you look for refuge you should look at your own intentional actions right here & now.

It is said that the outcome of your actions do not necessarily entail the same exact thing happening to you, but that skillful karma leads to pleasant results while unskillful karma leads to unpleasant results, down the line.

The answer to your question boils down to the answer to the following question: Is it me or someone else paying karma for my sins?

Essentially, individual karma is a simplified model, useful to beginners but somewhat misleading. Karma is simply action and its resulting circles on the water of experience, with not-yet-manifested result "stored" in the form of intermediate already-manifested result. Some of that is "stored" as effect on the so-called "mind", and some as effect on the so-called "objective" world. If we discount the delineation of independent agents (which too is a simplified model), what remains is action and its experienced result, both the action and the experience usually appropriated as "mine". To ask whether it is the same "me" or a different "me" is meaningless because this "me" does not exist in the first place.

More practically, one becomes victim of one's own karma (e.g. violence) by shaping the circumstances that tend to be conducive to the same karma being repeated. Because karma and its circumstances are two sides of the same coin, one produces the other. For example, by making violence part of one's life one shapes circumstances in which violence is more likely to occur, which increases the chances of one becoming its victim.

I hope you read this answer first

How Karma is get paid

• When person is doing a Karma it is done among 17 Naama (karma Ruupa). Energy to transmit to next Ruupa is generated by 7 Jawan Naamas created in karma Ruupa(Ruupa that consist of Karma).
• Then when appropriate environment is there for get punished (Punishment can be good or bad due to the chethana(Intention) chithasika(Aspect, attribute of Nama) in the Karma Ruupa).
• It will generate Karma wipaka(Result) Ruupa according to the chethana chithasika that consist of feelings to the creature appropriate to chethana.
• So it matters only time to generate Karma wipaka when Karma is done.

Karma is facilitated by emptiness. Because we are empty of essence, each choice and action you make leaves an imprint on your mind that, like all things, decays over time. So, if you make a negative action, you leave a negative imprint on your mind. Now, since we are empty of essence, you are more likely to perform actions with similar characteristics to the ones you have performed before. The more negative actions you choose to make, the more negative and troubled you become. This is why mindfulness and all the right stuff (view, speech, etc) is crucial. You have no nature other than what you choose and what you surround yourself with. If you let all that negativity build up by not being mindful of your actions and choosing rightly, you're going to have a lot of work to do towards purification.

Now, how does that relate to others in the way you're asking? Well it turns out that everything is empty of essence. Therefore beyond your mind, you leave an imprint on the world with similar characteristics as your actions, thus encouraging others to act in a similar way. And since you're inseparable from this gloriously intertwined existence, you are likely to reap what you've sewn.