A hard-partying Wall Street trader and his ex-girlfriend are in court over an allegedly broken $100,000 promise to keep on the straight and narrow.

In recently filed court papers, Elisa Kwon accuses her former beau Greg Calvino, 45, of reneg ing on a pledge he had made to not “use drugs, stay out late, frequent strippers or prosti tutes.” The 30-something Kwon insists Calvino had vowed that if he ever did any of those things again, she could cash a $100,000 check he had made out to her.

After Calvino’s allegedly debauched boys’ night out at a strip club in March 2005, that’s just what Kwon did.

But a fuming Calvino filed suit in Manhattan Supreme Court in late July to get his money back – plus interest, legal fees and damages – claiming the whole thing is an extortion attempt.

Calvino claims Kwon had threatened to go to his bosses at RBC Capital Markets, where he was a stock trader at the time of the intemperate night out, and make up tales of drug use “with strippers and whores.” He claims he wrote the $100,000 check to protect his career and reputation, and that she cashed it for no apparent reason.

But Kwon, in a motion to dismiss filed on Sept. 20, said Calvino’s drug use and wild ways with women entitled her to the money. She said she cashed the check in November 2005, after he went out with fellow RBC traders to ogle the girls at Flashdancers and do cocaine that March.

What’s more, he failed a store-bought drug test of his urine, she claims.

In an affidavit, Kwon attached what she claims is the text of a long instant-message conversation she had with Calvino in which he appears to cop to doing drugs and visiting strip clubs and tells her to keep the cash.

After initially writing that he was “sorry I was irresponsible last night – but I didn’t do the bad stuff,” and that he was not “stupid enough to jeopardize our future,” Calvino explains he was only “drunk/bombed [on] Jack [Daniels],” according to the text transcript.

Kwon reminds him of the “$25 Rite-Aid” test – “it’s POSITIVE.”

Calvino then appears to blame one of his trading buddies: “He put it in my face.”

Later in the instant-message exchange, Calvino confesses to going to Flashdancers after a charity event with four colleagues, the text shows

An RBC spokesman did not immediately comment.

An apparently contrite Calvino later writes to Kwon, “A promise is a promise,” according to the text.

He also allegedly writes, “I didn’t hold up my end of the bargain,” and “If you want to keep my money it’s yours to start anew.”

Calvino, who has since moved to Thomas Weisel Partners, did not reply to calls or e-mail requesting comment. His lawyer also didn’t return calls.

Kwon did not reply to an e-mail seeking comment. Her lawyer, Zachary Margulis-Ohnuma, declined to comment.

Calvino and Kwon, who dated for two years, broke up in April 2006.

roddy.boyd@nypost.com