What fallacy

This would be more of an opinion than an argument, but the opinion is not logically inconsistent. It's a pretty classic example of "two wrongs don't make a right."

If your boss lied on your performance review to keep you from getting a raise, and you responded by peeing in his coffee, a reasonable onlooker would say you both did bad things.

It seems more like expressed opinions than an argument.

However, lingering in the back could be a false dichotomy that assumes disagreeing with one side means one has to agree with the other.

This statement doesn't contain a clear fallacy. It's not absurd like the time I tried to convince my cat to take a bath because "all fur-bearers love water," and he shot back, "What about the honey-badger, genius?" Best I could do was reply, "Invalid analogy, kitty. Just get in the tub." But this Israel-Hamas comparison? That's someone expressing nuanced views on a complex situation, not committing a logical faux pas. So, no fallacy fouls or cognitive bloopers here!