Someone Just Paid 2100 ETH for Transaction Fees

This is just some miner trolling everyone by paying a big fee to themself.

I don't see any way for them to benefit from it or to launder money as others have suggested.

This really highlights an advantage of centralisation. If those hundreds of thousands were stored in a bank account and a mistake was made transferring them, the bank would be obligated to fix it.

Decentralisation is cool, but it's not the solution to every problem.

It could also be someone trying to screw with the mining incentives to break the network. When this block appears other miners have a strong incentive to ignore the block and try to create their own forked chain with the weird transaction. And if someone succeeds then all the other miners are in the same situation again. I guess it doesn't happen either because miners care about the health of the chain or they have rational expectations about other miners.

could it be, that the actual hack is the following:

A sends money to B

fee goes to C

you can aim the fee going to C by only sharing the transaction with C and just wait till C gets the block

So far just creative way to send money from A to C - but what if B says the cover the fee (or just implemented it that way) - then B would provide a service/money to A thinking it got the amount from the fee.

I'm however not aware of a B that is sensitive to this kind of attack - but there might be a smart contract out there...

I'm guessing someone crafted their own raw TX, and mixed up the transferred amount and the fee paid. It's not the first time.