Olivia Culpo Rocks Danny Amendola's Birthday Rolex in Skin-Tight Leather Pants

Olivia Culpo wasn't lyin' when she said she was keeping Danny Amendola's birthday present ... rockin' her ex's $12,000 Rolex and a bad ass leather outfit in Miami!!

The gorgeous model shaded the Dolphins star on social media after he was spotted flirting with a sports reporter on the beach last month ... saying she was gonna keep the flashy watch for herself.

Not only was O.C. sporting her ex-boo's ex-birthday present ... she was wearing skin-tight leather pants that would make Olivia Newton-John's "Grease" character jealous ... along with a black hoodie, leather jacket and black beanie.

As for Culpo's next move ... it sounds like she's not jumping right back onto the dating scene ... telling reporters at the CMA Awards she's not looking for a replacement just yet.