All Rihanna wanted for Christmas was an autograph — on her breast, from Mariah Carey, right after the latter’s hotly anticipated Brooklyn holiday concert.

The Fenty founder, 36, flagged down the “All I Want for Christmas Is You” crooner, 55, at the end of her Barclays Center Christmas show Tuesday to request an autograph on her boob. Podcaster and “Love & Hip Hop: Hollywood” alum Jason Lee joked that “Rocky made us do it,” in a nod to Rihanna’s longtime partner, A$AP Rocky, with whom she shares two young sons.

A guard escorted Carey over to the “Diamonds” singer and, after some back and forth about Rihanna’s sunglasses and whether she was filming Carey on her “bad side,” Rihanna requested her fellow Grammy winner “sign my tit.”

“What do you want me to write?” Carey asked as she got into position.

“‘Mariah.’ What the f–k do you think?” Rihanna quipped, then saying she could write “whatever you want. Wow, this is iconic.”

Rihanna grabbed the microphone and announced to the crowd, “Mariah Carey is signing my tit, y’all. … Oh! Look at that s–t.”

Carey’s concert hadn’t been a certainty in recent days as she contended with the flu.

Carey canceled two shows last weekend at Newark’s Prudential Center and Elmont’s UBS Arena as well as a show in Pittsburgh earlier in the week due to illness.

Though Rihanna keeps making waves in fashion and beauty, and has long remained quiet on the music front, her outings — particularly those with Harlem-born Rocky, also 36 — reliably excite fans and onlookers alike.

The A-list couple was seen getting silly and cozy earlier this month at the 38th Annual Footwear News Achievement Awards hosted at Manhattan’s Casa Cipriani. There, Rocky won a Collaboration of the Year Award for his work with Puma.