That's interesting, as being a non-native English speaker I always assumed it was one of the accepted meanings. So as every time I realize one of these things, let's check the Wiktionary entry for soak:

Verb

soak (third-person singular simple present soaks, present participle soaking, simple past and past participle soaked)

4. (transitive) To allow (especially a liquid) to be absorbed; to take in, receive. (usually + up)

   I soaked up all the knowledge I could at university.

So yes, even though it is not the most often used meaning, "to soak" can be used for "to absorb", and not only for liquids. So "soaking damage" for "receiving damage and absorbing it" is not a pure invention, it is accepted - though unusual - English language.

Rules lawyer/Back-seat DM are pretty close

Rules lawyer is the term for someone who constantly enforces the precise letter of the rules in games even going so far as to correct and try to argue with DMs and other players.

Back-seat DM is similar, but they often try to control other things like adherence to lore and over-stepping with unsolicited suggestions about how the game should be run including: how NPCs should be acting, what should be happening in plot, etc. Basically they try to be the DM and control DM things when they are not the DM.

It sounds like this player could be described as both or a mixture of the two terms.

Sidenote: That isn't even what murderhobo means

I'm not sure this player understands what the term murderhobo means, but they appear to be using it incorrectly.

From Wiktionary:

A player character who wanders the game world widely, has no ties or obligations, and approaches most obstacles violently.

So this doesn't really mean anything about breaking rules or ignoring lore at all.

Calling names is not going to solve this issue

You are asking here for a way to stop this bickering, calling this person names is not going to help the situation at all regardless if the name is "rules-lawyer" or "back-seat DM" or "zorkmorking clorbag". If calling names doesn't escalate the situation (likely) it will simply do nothing. Many such people wear such names as badges of honor.

No, your solution is going to have to come from addressing the social contract at your table and it will have to be lead by your DM. Talk to your DM privately and tell them how this player is affecting your and the other players' enjoyment of the game and ask them to try to address it.

It is important to note that since this player is new, maybe the expectation that they not do this was not made clear and maybe it was a different way at the last tables they played at.

If the DM agrees that it is an issue that they want to address, the DM can then clearly lay down the expectation that the DM is in charge of rules and lore at the table and that, small corrections aside, any major objections should be brought to their attention after the game where they can be addressed without interrupting the game or affecting enjoyment.

We have lots of questions that address this issue. See this and this to start.