"LuAnn's decided she doesn't want to sing. I don't blame her. She's not that great. And guess what? There's no Auto-Tune here," Singer quipped in Tuesday night's episode, after Thomson informed her that the countess would not be performing at the iconic jazz club Birdland.
Singer then told de Lesseps upon her entrance, "I'm upset you're not singing tonight."
"It's Mario's night," she replied, later adding, "I didn't want to show him up."
But Singer delivered her patented stinger: "You're afraid to sing because you don't have Auto-Tune."
"I can do whatever I want, and if I feel like singing I will," said de Lesseps.
But she didn't, which only heightened Singer's ire.
"Why did you back out?" she asked again. "Mario learned his song in one day."
"Shut your face," countered the countess, who continued to engage in an angry verbal volley with Singer. "Ramona loves to pick on me and bully me."
When the two stopped jabbing, Mario took the stage, singing a love ballad to his wife.
"Effortless," Mario ironically crooned to his teary-eyed wife, who filed for divorce in January from her husband of 22 years but now may be reuniting with him.
"Was he Frank Sinatra?" asked the countess, getting in the final dig. "No."
But Thomson surprised the wives by singing an energetic rendition of "Bill Bailey, Won't You Please Come Home" as a tribute to her musician father.
"Is there nothing Heather can't do?" asked Kristen Taekman, who felt she could do nothing right for her husband, Josh, after he yelled at her when she called him at work to find out why he was running so late for a dinner she had made for him.
"I was in the middle of a conference call with six different people!" he bellowed. "I don't have time to send you a text!"
"I don't understand why he can be on time for a business associate but not his wife," she said, later telling him after he belittled her cooking, "I can't stand when you mock me. Why do you push my buttons?"
"You lose sight of why you fell in love," continued an emotional Taekman, whose husband finally agreed to see a therapist.
The Real Housewives of New York City airs Tuesdays (9 p.m. ET) on Bravo.