Infinite regress and debunking karma

[Belacqua]

According to the theory of Karma, all suffering is caused by your own misdeeds (any acts causing suffering to others) in a past life or this life.

Let's call the first being to ever suffer Bob.

According to the theory of Karma, Bob must have done something in a past life or this life which caused someone else to suffer.

This means that someone else suffered before Bob ever suffered, which contradicts our assumption that Bob was the first being to ever suffer. 

We started with two premises (Karma is real, there was a being who was the first to ever suffer) and arrived at a contradiction, which means that one of the premises must be false. 

I can't see a reason not to assume that there was indeed a first being to ever suffer, so therefore the premise which must be discarded is the premise that karma is real.

By a proof by contradiction I've shown that the theory of karma must be incorrect.

There are SO MANY variations in the different schools which teach about karma, that we probably can't find a definitive answer. I can think of two responses to your question which might be relevant.

First, we mustn't be overly determinist about karma. It doesn't cause absolutely everything that happens to us. So even before Bob did anything to deserve suffering, he may have just had bad luck. Again, there's variation in the schools, but I don't think they say that it's a one-to-one deal. In fact it would be unfair for us to assume that someone suffering now must have been bad before; we don't really know.

Second, bad karma can be accumulated from bad intent as well as from bad action. Like if you try your best to commit genocide but you don't bring it off, you still get bad karma. So it's possible that in a past life Bob tried but failed to cause suffering. He'd still get the hammer dropped on him later on. 

I'm not saying I believe all this. Just that it would address the logical dilemma you raise.