Promissary Note by Coercion

need information on whether a promissary note that was signed after being given alcohol and verbally threatened.
boyfriend out of 8 year relationship. ex-girlfriend gave him authorization to use mastercard during 8 yrs. now ex wants reimbursement for now "unauthorized use of card". he was not removed from card until after relationship dissolved. she now shows up with request for signature on promissary note for $7k of charges + interest. states she needs it for tax purposes. when he refused to sign, she gave him alchol and then treatened to make his life hell starting by humiliating him in public restaurant. So in the confusion, he signed it to get her to stop the scene. Will this document hold up in court now that she is demanding payments? She has failed to produce verification of unauthorized charges if he was authorized to use. the mastercard company is not interested in her stupidity nor will they transfer debt since she authorized him to use. she is now threatening him with court action. does this document hold water for her based on how she got the signature and in front of witnesses?