Let me explain: The humor in this comic strip lies in the absurdity as well as the "comedic timing" in the pacing of the individual panels. The symbol at the start clearly depicts a very minimalist version of a person on a bike. The comic however "takes it literally" and imagines a person driving around with only two wheels, one of which runs between their butcheeks (also a "funny part" of the human body). It doesn't show this right away but contrasts two panels where "nothing happens" with the sudden appearance of this... Thing. It gradually reveals three funny things: First, the absurd thought that what is shown in the symbol is literally what is happening, as explained before. Second, the wheel running through the butcheeks, and lastly, that the person doing this is suffering. This means, there must be some even more absurd circumstances that lead to this whole situation.

I hope I could explain to you how this is funny. Although jokes notoriously die while being dissected.

Edit: aaaaaand the comment is gone.