How to deal with this guy who won't stop texting?

He's the brother of a work colleague. Every day he messages "hello, how are you darling" . I just reply with 'I'm good thanks.

. The last text he sent was 'I'm good with my tongue " So I ignored him, but every day he keeps texting "how are you '. What's the best way to deal with it. Someone told me he's mentally unstable. So not sure how to deal with it.

How to deal with this guy who won't stop texting?
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