Nasty recruiter during salary negotiation

I got an offer from a big healthcare company and tried to negotiate for 15% increase in base salary. Recruiter was very snarky and said things like: the offer is firm. ABC (not real name) is a world class institution with world class benefits and you are not happy with the offer? You are not even working right now. I’m extremely put off. Told him i need a few more days. But most likely will reject this offer. Any advice on what else i should do? Thanks!

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