You may seek a criminal court order of protection if the tenant is objectively harassing and endangering you. You may want to consult with an experienced landlord tenant lawyer to see if you can sue the landlord for jot providing you with the quiet enjoyment of your apartment. Suing the other tenant is an option, though it may be costly and time consuming.
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New York does not have a civil cause of action for harassment. I suggest you consult a landlord/tenant lawyer to see if you have a claim against the landlord for failing to enforce the warranty of habitability.
I am a former federal and State prosecutor and now handle criminal defense and personal injury/civil rights cases. Feel free to check out my web site and contact me at (212) 577-9797 or via email at Eric@RothsteinLawNY.com. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. The above answer is for informational purposes only and not meant as legal advice.
New York does have a civil cause of action for nuisance, but you're unlikely to find an attorney willing to pursue a case like this on a contingency basis.
If you'd like to discuss, please feel free to call. Jeff Gold Gold, Benes, LLP 1854 Bellmore Ave Bellmore, NY 11710 Telephone -516.512.6333 Email - Jgold@goldbenes.com